Composite solid polymer electrolyte membranes

ABSTRACT

The present invention relates to composite solid polymer electrolyte membranes (SPEMs) which include a porous polymer substrate interpenetrated with an ion-conducting material. SPEMs of the present invention are useful in electrochemical applications, including fuel cells and electrodialysis.

This application is a continuation-in-part of International ApplicationPCT/US98/17898 filed Aug. 28, 1998, which was a continuation-in-part ofU.S. Provisional Application No. 60/057,233, filed Aug. 29, 1997.

STATEMENT OF GOVERNMENT RIGHTS

This invention was made with Government support under Contract No.DE-FC02-97EE50478 awarded by the Department of Energy and Contract No.DMI-9760978 with National Science Foundation. The Government has certainrights in this invention.

FIELD OF THE INVENTION

This invention relates to novel composite solid polymer electrolytemembranes (SPEMs) for use in electrochemical applications. Methods forproducing the composite membranes of the invention are also disclosed.

BACKGROUND OF THE INVENTION

There is a considerable need in both the military and commercial sectorsfor quiet, efficient and lightweight power sources that have improvedpower density. Military applications include, but are not limited to,submersibles, surface ships, portable/mobile field generating units, andlow power units (i.e., battery replacements). For example, the militaryhas a strong interest in developing low range power sources (a few wattsto a few kilowatts) that can function as replacements for batteries.Commercial applications include transportation (i.e., automotive, bus,truck and railway), communications, on-site cogeneration and stationarypower generation.

Other interest exists for household applications, such as radios,camcorders and laptop computers. Additional interest exists in largerpower sources or sources of higher power density that can be used inoperating clean, efficient vehicles. In general, there is a need forquiet, efficient and lightweight power sources anywhere stationary powergeneration is needed.

Additionally, the use of gasoline-powered internal combustion engineshas created several environmental, exhaust gas-related problems. Onepossible solution to these environmental problems is the use of fuelcells. Fuel cells are highly efficient electrochemical energy conversiondevices that directly convert the chemical energy derived from renewablefuel into electrical energy.

Significant research and development activity has focused on thedevelopment of proton-exchange membrane fuel cells. Proton-exchangemembrane fuel cells have a polymer electrolyte membrane disposed betweena positive electrode (cathode) and a negative electrode (anode). Thepolymer electrolyte membrane is composed of an ion-exchange polymer(i.e., ionomer). Its role is to provide a means for ionic transport andprevent mixing of the molecular forms of the fuel and the oxidant.

Solid polymer electrolyte fuel cells (SPEFCs) are an ideal source ofquiet, efficient, and lightweight power. While batteries have reactantscontained within their structure which eventually are used up, fuelcells use air and hydrogen to operate continuously. Their fuelefficiency is high (45 to 50 percent), they do not produce noise,operate over a wide power range (10 watts to several hundred kilowatts),and are relatively simple to design, manufacture and operate. Further,SPEFCs currently have the highest power density of all fuel cell types.In addition, SPEFCs do not produce any environmentally hazardousemissions such as NO_(x) and SO_(x) (typical combustion by-products).

The traditional SPEFC contains a solid polymer ion-exchange membranethat lies between two gas diffusion electrodes, an anode and a cathode,each commonly containing a metal catalyst supported by an electricallyconductive material. The gas diffusion electrodes are exposed to therespective reactant gases, the reductant gas and the oxidant gas. Anelectrochemical reaction occurs at each of the two junctions (threephase boundaries) where one of the electrodes, electrolyte polymermembrane and reactant gas interface.

During fuel cell operation, hydrogen permeates through the anode andinteracts with the metal catalyst, producing electrons and protons. Theelectrons are conducted via an electrically conductive material throughan external circuit to the cathode, while the protons are simultaneouslytransferred via an ionic route through the polymer electrolyte membraneto the cathode. Oxygen permeates to the catalyst sites of the cathode,where it gains electrons and reacts with protons to form water.Consequently, the products of the SPEFC's reactions are water,electricity and heat. In the SPEFC, current is conducted simultaneouslythrough ionic and electronic routes. Efficiency of the SPEFC is largelydependent on its ability to minimize both ionic and electronicresistivity to these currents.

Ion exchange membranes play a vital role in SPEFCs. In SPEFCs, theion-exchange membrane has two functions: (1) it acts as the electrolytethat provides ionic communication between the anode and cathode; and (2)it serves as a separator for the two reactant gases (e.g., O₂ and H₂).In other words, the ion-exchange membrane, while serving as a goodproton transfer membrane, must also have low permeability for thereactant gases to avoid cross-over phenomena that reduce performance ofthe fuel cell. This is especially important in fuel cell applications inwhich the reactant gases are under pressure and the fuel cell isoperated at elevated temperatures.

Fuel cell reactants are classified as oxidants and reductants on thebasis of their electron acceptor or electron donor characteristics.Oxidants include pure oxygen, oxygen-containing gases (e.g., air) andhalogens (e.g., chlorine). Reductants include hydrogen, carbon monoxide,natural gas, methane, ethane, formaldehyde and methanol.

Optimized proton and water transports of the membrane and proper watermanagement are also crucial for efficient fuel cell application.Dehydration of the membrane reduces proton conductivity, and excesswater can lead to swelling of the membranes. Inefficient removal ofby-product water can cause flooding of the electrodes hindering gasaccess. Both of these conditions lead to poor cell performance.

Despite their potential for many applications, SPEFCs have not yet beencommercialized due to unresolved technical problems and high overallcost. One major deficiency impacting the commercialization of the SPEFCis the inherent limitations of today's leading membrane and electrodeassemblies. To make the SPEFC commercially viable (especially inautomotive applications), the membranes employed must operate atelevated/high temperatures (>120° C.) so as to provide increased powerdensity, and limit catalyst sensitivity to fuel impurities. This wouldalso allow for applications such as on-site cogeneration (high qualitywaste heat in addition to electrical power). Current membranes alsoallow excessive methanol crossover in liquid feed direct methanol fuelcells (dependent on actual operating conditions, but is typicallyequivalent to a current density loss of about 50 to 200 mA/cm²@ 0.5V).This crossover results in poor fuel efficiency as well as limitedperformance levels.

Several polymer electrolyte membranes have been developed over the yearsfor application as solid polymer electrolytes in fuel cells. However,these membranes have significant limitations when applied to liquid-feeddirect methanol fuel cells and to hydrogen fuel cells. The membranes intoday's most advanced SPEFCs do not possess the required combination ofionic conductivity, mechanical strength, dehydration resistance,chemical stability and fuel impermeability (e.g., methanol crossover) tooperate at elevated temperatures.

DuPont developed a series of perfluorinated sulfonic acid membranesknown as Nafion® membranes. The Nafion® membrane technology is wellknown in the art and is described in U.S. Pat. Nos. 3,282,875 and4,330,654. Unreinforced Nafion® membranes are used almost exclusively asthe ion exchange membrane in present SPEFC applications. This membraneis fabricated from a copolymer of tetrafluoroethylene (TFE) and aperfluorovinyl ethersulfonyl fluoride. The vinyl ether comonomer iscopolymerized with TFE to form a melt-processable polymer. Once in thedesired shape, the sulfonyl fluoride group is hydrolyzed into the ionicsulfonate form.

The fluorocarbon component and the ionic groups are incompatible orimmiscible (the former is hydrophobic, the latter is hydrophilic). Thiscauses a phase separation, which leads to the formation ofinterconnected hydrated ionic “clusters”. The properties of theseclusters determine the electrochemical characteristics of the polymer,since protons are conducted through the membrane as they “hop” from oneionic cluster to another. To ensure proton flow, each ionic group needsa minimum amount of water to surround it and form a cluster. If theionic group concentration is too low (or hydration is insufficient)proton transfer will not occur. At higher ionic group concentrations (orincreased hydration levels) proton conductivity is improved, butmembrane mechanical characteristics are sacrificed.

As the membrane temperature is increased, the swelling forces (osmotic)become larger than the restraining forces (fluorocarbon chains). Thisallows the membrane to assume a more highly swollen state, but mayeventually promote membrane dehydration. Peroxide radicals will formmore quickly as the temperature is increased; these radicals can attackand degrade the membrane. At even higher temperatures (230° C.), thefluorocarbon phase melts and permits the ionic domains to “dissolve”(phase inversion of Nafion®).

There are several mechanisms that limit the performance of Nafion®membranes in fuel cell environments at temperatures above 100° C. Infact, these phenomenon may begin at temperatures above even 80° C.Mechanisms include membrane dehydration, reduction of ionicconductivity, radical formation in the membrane (which can destroy thesolid polymer electrolyte membrane chemically), loss of mechanicalstrength via softening, and increased parasitic losses through high fuelpermeation.

Crossover problems with Nafion® membranes are especially troublesome inliquid feed direct methanol fuel cell applications, where excessivemethanol transport (which reduces efficiency and power density) occurs.Methanol-crossover not only lowers fuel utilization efficiency but alsoadversely affects the oxygen cathode performance, significantly loweringcell performance.

The Nafion® membrane/electrode is also very expensive to produce, and asa result it is not (yet) commercially viable. Reducing membrane cost iscrucial to the commercialization of SPEFCs. It is estimated thatmembrane cost must be reduced by at least an order of magnitude from theNafion® model for SPEFCs to become commercially attractive.

Another type of ion-conducting membrane, Gore-Select® (commerciallyavailable from W.L. Gore), is currently being developed for fuel cellapplications. Gore-Select® membranes are further detailed in a series ofU.S. Patents (U.S. Pat. Nos. 5,635,041, 5,547,551 and 5,599,614).

Gore discloses a composite membrane consisting of a porous Teflon® filmfilled with a Nafion® or Nafion®-like ion-conducting solution. Althoughit has been reported to show high ionic conductance and greaterdimensional stability than Nafion® membranes, the Teflon® and Nafion®materials selected and employed by Gore as the film substrate and theion-exchange material, respectively, may not be appropriate foroperation in high temperature SPEFCs. Teflon® undergoes extensive creepat temperatures above 80° C., and Nafion® and similar ionomers swell andsoften above the same temperature. This can result in the widening ofinterconnected channels in the membrane and allow performancedegradation, especially at elevated temperatures and pressures.

Further, Gore-Select®, as well as many other types of perfluorinatedion-conducting membranes (e.g., Aciplex from Asahi Chemical, Flemion®from Asahi Glass, Japan), are just as costly as Nafion®, since thesemembranes employ a high percentage of perfluorinated ionomers.

In an effort to reduce costs and move toward potential commercializationof SPEFCs, ion-exchange membranes that are less expensive to producealso have been investigated for use in polymer electrolyte membrane fuelcells.

Poly(trifluorostyrene) copolymers have been studied as membranes for usein polymer electrolyte membrane fuel cells. See e.g., U.S. Pat. No.5,422,411. However, these membranes are suspected to have poormechanical and film forming properties. In addition, these membranes maybe expensive due to the inherent difficulties in processing fluorinatedpolymers.

Sulfonated poly(aryl ether ketones) developed by Hoechst AG aredescribed in European Patent No. 574,891,A2. These polymers can becrosslinked by primary and secondary amines. However, when used asmembranes and tested in polymer electrolyte membrane fuel cells, onlymodest cell performance is observed.

Sulfonated polyaromatic based systems, such as those described in U.S.Pat. Nos. 3,528,858 and 3,226,361, also have been investigated asmembrane materials for SPEFCs. However, these materials suffer from poorchemical resistance and mechanical properties that limit their use inSPEFC applications.

Solid polymer membranes comprising a sulfonated poly(2,6 dimethyl 1,4phenylene oxide) alone or blended with poly(vinylidene fluoride) alsohave been investigated. These membranes are disclosed in WO 97/24777.However, these membranes are known to be especially vulnerable todegradation from peroxide radicals.

The inherent problems and limitations of using solid polymer electrolytemembranes in electrochemical applications, such as fuel cells, atelevated/high temperatures (>100° C.) have not been solved by thepolymer electrolyte membranes known in the art. Specifically,maintaining high ion conductivity and high mechanical strength,resisting dehydration and other forms of degradation remain problematic,especially at elevated operating temperatures. As a result,commercialization of SPEFCs has not been realized.

It would be highly desirable to develop an improved solid polymerelectrolyte membrane with high resistance to dehydration, highmechanical strength and stability to temperatures of at least about 100°C., more preferably to at least about 120° C.

It would also be highly desirable to develop a membrane with theafore-mentioned characteristics that would be suitable for use in ahydrogen or methanol fuel cell and that would provide an economicaloption to currently available membranes. The development of such amembrane would promote the use of SPEFCs in a variety of highly diversemilitary and commercial applications, and would be beneficial toindustry and to the environment.

SUMMARY OF THE INVENTION

The present invention provides innovative solid polymer electrolytemembranes that are capable of operating at much higher temperatures andpressures than those known in the art. Methods for producing suchmembranes are also provided. The membrane manufacturing technologiesdeveloped emphasize improved performance at reduced cost.

A central object of the invention is to provide an improved solidpolymer electrolyte membrane (SPEM) having the followingcharacteristics: high ionic conductivity, high resistance todehydration, high mechanical strength, chemical stability duringoxidation and hydrolysis, low gas permeability to limit parasiticlosses, and stability at elevated temperatures and pressures.

Another object of the invention is to provide an improved solid polymerelectrolyte membrane with electronic conductivity approaching zero,dimensional stability, and a membrane that is non-brittle in both dryand wet forms.

Another object of the invention is to provide an improved solid polymerelectrolyte membrane that is resistant to methanol cross-over when usedin a direct methanol fuel cell.

Another object of the invention is to substantially lower the overallcost of producing solid polymer electrolyte membranes to allow forcommercialization of SPEFCs.

A further object of the invention is to provide methods that can beemployed to produce these solid polymer electrolyte membranes.

Another object of this invention is to provide novel polymer substratesand ion-conducting materials and novel combinations thereof.

Yet another object of the present invention is to provide SPEMs that aresubstantially stable to temperatures of at least about 100° C.,preferably to at least about 150° C., more preferably to at least about175° C.

Foster-Miller has discovered that a high performance SPEM, suitable foruse in fuel cells, can be produced by interpenetrating a porous polymersubstrate with an ion-conducting material to form a composite membrane.This composite ion-conducting membrane will exhibit the strength andthermal stability of the polymer substrate and the ionic conductivity ofthe ion-conducting material.

The composite SPEM of the present invention comprises a porous polymersubstrate that is interpenetrated with an ion-conducting material.

The present invention also provides novel substrates and novelsubstrate/ion-conducting material combinations. These materials can betailored and combined to produce membranes useful over a range ofoperating conditions and/or applications.

Preferred polymer substrates are easily synthesized fromcommercially-available, low-cost starting polymers, into thin,substantially defect free polymeric films which have high strength evenat low thickness (in preferred embodiments less than about 1 mil),outstanding crease/crack resistance and high tear strength. Preferredpolymer substrates are substantially chemically resistant to acids,bases, free radicals and solvents (e.g., methanol) and are thermally andhydrolytically stable from temperatures of about 50° C. to 300° C. Inpreferred embodiments, the polymer substrates are thermally andhydrolytically stable to temperatures of at least about 100° C.

Preferred polymer substrates possess exceptional mechanical properties(much greater than about 2500 psi tensile, much less than about 100%elongation to break), dimensional stability, barrier properties (tomethanol, water vapor, oxygen and hydrogen) even at elevatedtemperatures and pressures and exceptional gauge uniformity (+/−0.2 milspreferable).

Preferred polymer substrates have a pore size range of 10 Å to 2000 Åmore preferably 500 Å to 1000 Å, and have a porosity range from about40% to 90%.

In some preferred embodiments of the present invention, the polymersubstrate of the SPEM comprises a lyotropic liquid crystalline polymer,such as a polybenzazole (PBZ) or polyaramid (PAR or Kevlar®) polymer.Preferred polybenzazole polymers include polybenzoxazole (PBO),polybenzothiazole (PBT) and polybenzimidazole (PBI) polymers. Preferredpolyaramid polymers include polypara-phenylene terephthalimide (PPTA)polymers.

In other preferred embodiments, the polymer substrate of the SPEMcomprises a thermoplastic or thermoset aromatic polymer. Preferredaromatic polymers include: polysulfone (PSU), polyimide (PI),polyphenylene oxide (PPO), polyphenylene sulfoxide (PPSO), polyphenylenesulfide (PPS), polyphenylene sulfide sulfone (PPS/SO₂),polyparaphenylene (PPP), polyphenylquinoxaline (PPQ), polyarylketone(PK) and polyetherketone (PEK) polymers.

Preferred polysulfone polymers include polyethersulfone (PES),polyetherethersulfone (PEES), polyarylsulfone, polyarylethersulfone(PAS), polyphenylsulfone (PPSU) and polyphenylenesulfone (PPSO₂)polymers. Preferred polyimide polymers include the polyetherimidepolymers as well as fluorinated polyimides. Preferred polyetherketonepolymers include polyetherketone (PEK), polyetheretherketone (PEEK),polyetherketone-ketone (PEKK), polyetheretherketone-ketone (PEEKK) andpolyetherketoneetherketone-ketone (PEKEKK) polymers.

Preferred ion-conducting materials for use in the fuel cells of thepresent invention are easily sulfonated or synthesized fromcommercially-available, low-cost starting polymers (or monomers), andare swellable, but highly insoluble in boiling water (100° C.) oraqueous methanol (>50%) over extended time periods.

Preferred ion-conducting materials have limited methanol permeability(limited methanol diffusivity and solubility) even at elevatedtemperatures and pressures, are substantially chemically stable to acidsand free radicals, and thermally/hydrolytically stable to temperaturesof at least about 100° C. Preferred ion-conducting materials have anion-exchange capacity (IEC) of >1.0 meq/g dry membrane (preferably, 1.5to 2.0 meq/g) and are highly ion-conducting (preferably, from about 0.01to about 0.5 S/cm, more preferably, to greater than about 0.1 S/cm or<10Ωcm resistivity).

Preferred ion-conducting materials are easily cast into films and/orimbibed into the porous polymer substrate. Such films are durable,substantially defect-free, and dimensionally stable (less than about 20%change in dimension wet to dry), preferably even above temperatures ofat least about 100° C. Particularly preferred ion-conducting materialshave the ability to survive operation in fuel cells (i.e., H₂/O₂,methanol) for at least about 5000 hours (e.g., automotive applications).

In one preferred embodiment of the present invention, the ion-conductingmaterial of the SPEM comprises a sulfonated, phosphonated orcarboxylated ion-conducting aromatic polymer. For example, it maycomprise a sulfonated derivative of at least one of the above-listedthermoset or thermoplastic aromatic polymers. It may also comprise asulfonated derivative of a polybenzazole or polyaramid polymer.

In an alternate embodiment, the ion-conducting material of the SPEM ofthe present invention comprises a non-aromatic polymer, such as aperfluorinated ionomer. Preferred ionomers include carboxylic,phosphonic or sulfonic acid substituted perfluorinated vinyl ethers.

Other preferred ion-conducting materials for use in the presentinvention include polystyrene sulfonic acid (PSSA), polytrifluorostyrenesulfonic acid, polyvinyl phosphonic acid (PVPA), polyvinyl carboxylicacid (PVCA) and polyvinyl sulfonic acid (PVSA) polymers, and metal saltsthereof.

Substrate and ion-conducting materials for use in the present inventionmay be substituted or unsubstituted and may be homopolymers, copolymersof the polymers listed above, or other blends. Any desired substituentsmay be incorporated into the classes of substrate and ion-conductingpolymers described herein for use in the present invention, providedthat such substituents do not substantially impair the propertiesdesired for the intended use of the polymer, as may readily bedetermined by one of ordinary skill in the art. Such properties mayinclude ionic conductivity, chemical and structural stability, swellingproperties and so forth. Blends could be of sulfonated (substituted)polymers or substituted/unsubstituted polymers.

The utility of blending polymers for the ion-conducting or the substratepolymers is in optimizing each of their properties. Unlike simplemixing, blending does not create a composite material with two dispersedcomponents. Rather, the blend is uniform in composition throughout. Inthe case of ion-conducting polymers, it might be useful to blend asulfonated polymer with an unsulfonated one to optimize swelling, fuelcrossover resistance, conductivity, peroxide resistance, hydrolyticstability and the like. Similarly, the blending of two sulfonatedpolymers might allow improved properties over each individual component.This concept can be extended to the substrate polymer, whereby blendingmay allow improvements in strength, cost, processability, or stability.

Representative formulae of unsubstituted polymers can be found in Tables4 to 7 at the end of the Detailed Description of the Invention.

Following selection of a suitable polymer substrate and ion-conductingmaterial in accordance with criteria set forth herein, one preferredmethod of fabricating a membrane of the present invention comprises thefollowing steps: solubilizing the ion-conducting material, preparing aporous substrate membrane, solvent exchanging the water swollenmembrane, imbibing the solvent swollen substrate with the ion-conductingmaterial via solution infiltration (such that the microinfrastructure ofthe porous polymer substrate is substantially interpenetrated with theion-conducting material). Upon solvent evaporation and drying, themicroporous substrate will collapse locking the ion-conductor within themicroinfrastructure of the polymer substrate. Post imbibing steps mayinclude tension drying, stretching and hot pressing of the compositemembrane. The substrate provides mechanical and chemical stability,while the ion-conductor provides a high-flux proton path. The SPEMs ofthe present invention also act as a barrier against fuel (H₂, O₂ andmethanol permeation) in fuel cell applications.

Another preferred method of producing the membranes of the presentinvention comprises the steps of preparing a mixture of the polymersubstrate and the ion-conducting material in a common solvent andcasting a composite membrane from the mixture.

Preferred solvents for these methods include tetrahydrofuran (THF),dimethylacetamide (DMAc), dimethylformamide (DMF), dimethylsulfoxide(DMSO), N-Methyl-2-pyrrolidinone (NMP), sulfuric acid, phosphoric acid,chlorosulfonic acid, polyphosphoric acid (PPA) and methanesulfonic acid(MSA). PPA and MSA are preferred solvents for a polymer substrate andion-conducting material combination of PBO/PPSU.

Another method of producing a membrane of the present inventioncomprises the steps of sulfonating the pores of the polymer substratewith a sulfonating agent.

Still another method for producing a composite membrane of the presentinvention comprises the steps of preparing the substrate polymer andsubsequently impregnating the substrate with appropriate monomers whichare then polymerized in-situ to form the composite SPEM.

Yet another method of producing a membrane of the present inventioncomprises the steps of preparing a mixture of a polymer substratematerial and an ion-conducting material and extruding a composite filmdirectly from the mixture.

The membranes of the present invention are useful in a variety ofelectrochemical devices, including fuel cells, electronic devices,systems for membrane-based water electrolysis, chloralkali electrolysis,dialysis or electrodialysis, pervaporation or gas separation.

The foregoing and other objects, features and advantages of theinvention will become better understood with reference to the followingdescription and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustrating the preparation of one type or methodof a composite membrane of the present invention.

FIG. 2 shows a graph of % dry loading of ICP/PBO vs. initial ICPsolution wt. % for Nafion®/PBO, sulfonated Radel R®/PBO and sulfonatedSulfide-Sulfone/PBO, in accordance with the present invention.

DETAILED DESCRIPTION

The composite membranes of the present invention are designed to addressthe present shortcomings of today's solid polymer electrolyte membranes,specifically Nafion® and other like membranes (e.g., Gore-Select®).

The present invention provides a relatively low cost, composite solidpolymer electrolyte membrane (SPEM), with improved power density andreduced sensitivity to carbon monoxide in hydrogen fuel. It may alsoalleviate water management problems which limit the efficiency ofpresent Nafion® membrane-based fuel cells.

The composite membranes of the present invention may be employed invarious applications, including but not limited to, polarity-basedchemical separations; electrolysis; fuel cells and batteries;pervaporation; reverse osmosis—water purification, gas separation;dialysis separation; industrial electrochemistry, such as choralkaliproduction and other electrochemical applications; water splitting andsubsequent recovery of acids and bases from waste water solutions; useas a super acid catalyst; use as a medium in enzyme immobilization, forexample; or use as an electrode separator in conventional batteries.

The composite SPEMs of the present invention comprise a porous polymersubstrate interpenetrated with an ion-conducting material. The porouspolymer substrate serves as a mechanically, thermally, chemically andoxidatively durable support for the ion-conducting material, e.g.,polymer. Ion-conducting polymers (ICPs) with very high ion-exchangecapacities (preferably, IEC>1.0 meq/g; more preferably, IEC 1.5-2.0meq/g) can be used in SPEMs of the present invention, since the strengthproperties of the ICP are not needed for membrane mechanical integrity.

The porous polymer substrate is characterized by a microinfrastructureof channels that have substantially uniform, unchanging dimensions (Tgis higher than use temperature). That is, the substrate material willnot flow, since the fuel cell operating temperature is less than the Tgof the substrate. The ion-conducting polymer substantiallyinterpenetrates the microinfrastructure of the porous polymer substrate.This configuration, which can be made quite thin, promotes efficientproton transport across the membrane and minimizes water managementproblems. As a consequence, eventual membrane dehydration, parasiticlosses and loss of ionic conductivity can be substantially prevented.

Preferably, thermally stable, wholly aromatic polymers are used inproducing the composite membranes of the present invention, but anymaterial(s) meeting the following requirements may generally be used:low cost, high ionic conductivity, electronically insulating,impermeable to fuel (H₂, O₂, methanol) at elevated temperatures andpressures in fuel cell applications, chemically resistant to acids,bases and free radicals, Tg above fuel cell operating temperature (atleast about 175° C. is preferred), minimal water transport rate duringoperation, resistance to puncture or burst during operation at hightemperatures and pressures, and maintenance of ionic conductivity atelevated/high operating temperatures.

The selection criteria for polymer substrates and ion-conductingmaterials suitable for SPEMs of the present invention are describedbelow. Structures for preferred polymer substrates and ion-conductingpolymers are indicated in Tables 4 to 7 which appear at the end of thissection.

Preferred polymer substrates are easily synthesized fromcommercially-available, low-cost starting polymers, into thin,substantially defect free polymeric films which have high strength evenat low thickness (preferably less than about 1 mil), outstandingcrease/crack resistance and high tear strength. Preferred polymersubstrates are substantially chemically resistant to acids, bases, freeradicals and solvents (i.e., methanol) and are thermally andhydrolytically stable from temperatures of about 50° C. to 300° C.Preferred polymer substrates possess exceptional mechanical properties(much greater than about 2500 psi tensile, much less than about 100%elongation to break), dimensional stability, barrier properties (tomethanol, water vapor, oxygen and hydrogen) even at elevatedtemperatures and pressures and exceptional gauge uniformity (+/−0.2 milspreferable). In preferred embodiments, the polymer substrates arethermally and hydrolytically stable to temperatures of at least about100° C.

Preferred polymer substrates have a pore size range of 10 Å to 2000 Åmore preferably 500 Å to 1000 Å, and have a porosity range from about40% to 90%.

In some preferred embodiments of the present invention, the porouspolymer substrate of the SPEM comprises a lyotropic liquid crystallinepolymer, such as a polybenzazole (PBZ) or polyaramid (PAR or Kevlar®)polymer. Preferred polybenzazole polymers include polybenzoxazole (PBO),polybenzothiazole (PBT) and polybenzimidazole (PBI) polymers. Preferredpolyaramid polymers include polypara-phenylene terephthalamide (PPTA)polymers. Structures of the above-mentioned polymers are listed in Table4.

In other preferred embodiments, the porous polymer substrate of the SPEMcomprises a thermoplastic or thermoset aromatic polymer. Preferredgroups of these aromatic polymers include the following: polysulfone(PSU), polyimide (PI), polyphenylene oxide (PPO), polyphenylenesulfoxide (PPSO), polyphenylene sulfide (PPS), polyphenylene sulfidesulfone (PPS/SO₂), polyparaphenylene (PPP), polyphenylquinoxaline (PPQ),polyarylketone (PK) and polyetherketone (PEK) polymers.

Preferred polysulfone polymers include polyethersulfone (PES),polyetherethersulfone (PEES), polyarylsulfone, polyarylethersulfone(PAS), polyphenylsulfone (PPSU) and polyphenylenesulfone (PPSO₂)polymers. Preferred polyimide polymers include the polyetherimidepolymers and fluorinated polyimides. Preferred polyetherketone polymersinclude polyetherketone (PEK), polyetheretherketone (PEEK),polyetherketone-ketone (PEKK), polyetheretherketone-ketone (PEEKK) andpolyetherketoneetherketone-ketone (PEKEKK) polymers. The structures ofthe above polymers are listed in Tables 5 and 6 below.

More preferably, the porous polymer substrate comprises a PBO or a PESpolymer. Most preferably, the porous polymer substrate comprises a PBOpolymer, such as a poly(bisbenzoxazole).

The PBO polymer is a member of a class of polymeric materialscollectively referred to as ordered polymers. As a result of its rigidrod-like molecular structure, PBO forms liquid crystalline solutionsfrom which extremely strong, stiff fibers and films have been processed.Foster-Miller has pioneered the development of innovative methods forprocessing PBO into microporous high-strength, high-modulusthermally-stable films that are useful for a multitude ofhigh-performance applications, e.g., in advanced aircraft andspacecraft.

When the PBO polymer is in a dry (entirely collapsed) form, it has thefollowing characteristics: high strength and dimensional stability,superior barrier (gaseous) properties, excellent crease/crackresistance, excellent tear strength, and superior thermal and hydrolytictemperature stability (>300° C.). Film-forming processes involve severaloperations in which a PBO polymer solution in polyphosphoric acidundergoes a succession of structural changes, leading to the finalproduct form. One basic process for producing PBO products includesextrusion of the polymer substrate solution (polymer and acid solvent),coagulation to lock-in the microstructure, washing to remove the acidsolvent, and drying (at high temperatures) to remove the exchanged waterand consolidate the polymer into the end product.

In one particularly preferred embodiment, the PBO film is extruded andmultiaxially oriented using a blown process as disclosed, e.g., in U.S.Pat. Nos. 4,939,235, 4,963,428 and 5,288,529 which are incorporatedherein by reference. The degree of multiaxial orientation can be variedfrom θ of ±5° to 65°, though an orientation of 22° to 30° is preferred.

During composite membrane fabrication, the following problems may beencountered: substrate film delamination, imbibtion of an insufficientamount of ion-conducting material inside the porous substrate and/orinability to maintain, if desired, a smooth outer layer ofion-conducting polymer for proper electrode bonding. These problems maybe overcome by heating of the ion-conducting polymer solution duringimbibtion into the substrate (which decreases the solution viscosity andswells the pores of the substrate) and using less oriented films (whichallows more ion-conducting material into the substrate).

The polymer substrate processing system includes a hydraulic flask,extruder, pump, counter-rotating die (CRD), porous sizing ring, waterwash tank/collapse shed and film take-up system. In one embodiment, thetake-up system includes a 3″ porous sizing ring followed by a 6″diameter take-up roll along with a 4″ diameter spooler. A number of CRDsand annular configurations may be used.

Information is collected and recorded for wet film thickness, dry filmthickness, draw ratio, blow-up ratio, overall film quality (veins, thinspots, voids, cracks, etc.) and extrusion system settings.

Samples (wet and dry) of PBO film from each extrusion run are thentested for tensile strength and tensile modulus, bubble point, pore sizedistribution, total pore volume and mean pore size.

Interestingly, smaller die gaps have been shown to cause greatershearing during extrusion, which results in fewer veins (defects) in thePBO film. High blow-up ratios also have resulted in improved films.Additionally, smaller die gaps and larger blow-up ratios increase PBOfibril orientation without the drawback of additional shear from dierotation (although torsional stress increases slightly).

In the coagulation stage, a liquid to solid phase transition is inducedby diffusion of a non-solvent (water) into the PBO solution. During thisphase transition cycle, the final structure of the solid is established.It is believed that the structure formed during the coagulation stage ofPBO fiber and film is an interconnected network of highly orientedmicrofibrils of 80 Å to 100 Å diameter. Such films have been dried undertension in order to produce high tensile properties. During the dryingprocess, the micropores present as spaces between microfibrils in PBOfilm undergo substantial shrinkage decreasing in dimensions from severalthousand Angstroms (e.g., 2000 Å) in size to less than 10 Å in size forthe dried, heat-treated PBO film. The final pore size depends highlyupon the heat treatment methods employed.

In forming a porous polymer substrate for the present invention, insteadof drying the water from the network, the water is replaced by thedesired ion-conducting material.

It has been discovered that a high performance PBO fuel cell membranecan be produced by interpenetrating or infusing the interior porosity ofwater-swollen PBO films with concentrated or dilute solutions ofion-conducting polymers, such as Nafion® or polyethersulfone sulfonicacid. For example, after the coagulated PBO film has been infiltratedwith a Nafion® solution, the Nafion® regions within the pores (andcoating on the surface) of the film will form a highlyionically-conducting gelatinous Nafion® membrane supported by the porousPBO membrane substrate. Such SPEMs exhibit the strength and thermalstability of PBO and the excellent ionic conductivity of water-swollenNafion(® copolymer.

The usual deficiencies of Nafion®, such as membrane weakness andsoftening at elevated temperatures, are improved by the PBO substrate tosupport against compression while simultaneously providing sufficientporosity to allow for adequate water content, thus enabling high protontransport. In preferred embodiments, the substrate will accommodateabout 40 to about 90 volume percent, preferably about 70 to about 80volume percent, of ion-conducting polymer.

As noted above, a second preferred polymer substrate comprises a PESpolymer. PES is a high use temperature amorphous thermoplastic thatexhibits long-term stability at elevated temperature (>175° C.). Themicroporous PES substrate represents a new class of high performancefuel cell membranes that can be used to solve the difficulties inherentin current Nafion® membranes as discussed above.

PES is readily available from Amoco Polymers, Inc. in Alpharetta, Ga.,USA, in large quantity at low cost. This polymer exhibits thecombination of desirable properties required for efficient function atmuch higher temperatures and pressures than are now possible(potentially greater than about 175° C. temperature and greater thanabout 100 psi gas pressure).

Microporous PES films for use in the SPEMs of the present invention canbe produced via standard film casting techniques or purchased directlyfrom appropriate vendors. As with other suitable polymer substrates, inone preferred embodiment, PES is dissolved in an appropriatewater-miscible solvent to a predetermined concentration. A solution ofPES is selected to produce a film with high porosity. The PES solutionis then cast onto glass plates to form a film, e.g., about 10 milsthick. Immersion of the plates in water coagulates the polymer andleaches out the solvent forming the microporous substrate membrane in awater swollen state. The ion-conducting polymer can then be introducedinto the microporous voids of the water swollen PES substrate membraneusing solvent exchange processes to form the composite membrane.Alternatively, the membrane can be dried first and then infiltrated withthe ion-conducting solution using vacuum to remove air bubbles and fillthe pores with ion-conducting polymer. The membrane may also be producedby an extrusion process as described herein.

Preferred ion-conducting polymers for use in the present invention areeasily sulfonated or synthesized from commercially-available, low-coststarting polymers, and are swellable, but highly insoluble in boilingwater (100° C.) or aqueous methanol (>50%) over extended time periods.Preferred ion-conducting polymers have limited methanol permeability(limited methanol diffusivity and solubility) even at elevatedtemperatures and pressures, are substantially chemically stable to acidsand free radicals, and thermally/hydrolytically stable to temperaturesof at least about 100° C. Preferred ion-conducting polymers have anion-exchange capacity (IEC) of >1.0 meq/g dry membrane (preferably, 1.5to 2.0 meq/g) and are highly ion-conducting (preferably, from about 0.01to about 0.5 S/cm, more preferably, to greater than about 0.1 S/cm or<10Ωcm resistivity). Preferred ion-conducting polymers are easily castinto films and/or imbibed into the polymer substrate. Such films aredurable, substantially defect-free, and dimensionally stable (less thanabout 20% change in dimension wet to dry) even above temperatures of atleast about 100° C. Preferred ion-conducting polymers have the abilityto survive operation in fuel cells (i.e., H₂/O₂, methanol) for at leastabout 5000 hours (e.g., automotive applications).

Preferred ion-conducting polymers are substantially chemically stable tofree radicals. The peroxide (H₂O₂) screening test serves as anaccelerated fuel cell life test. The test simulates long term fuel celloperation by exposing the subject aqueous ion-conducting membrane to aperoxide/iron solution at 68° C. for 8.0 hours. Under these conditions,aggressive hydroperoxide (HOO—) radicals are produced. It has been shownthat these radicals are formed during normal H₂/O₂ fuel cell operation,and are the prominent membrane degradation mechanism.

There are several methods to improve the long term stability (aqueoushydroperoxide radical) of PPSU (and other ion-conducting polymers inaccordance with this invention).

For example, the stability of the ion-conducting polymer may be enhancedby several post-processing steps. These steps include the following: (i)cross-linking the ion-conducting polymer in the H+ form to developsulfone crosslinks; (ii) addition of small amounts of antioxidants(insoluble) into the ion-conducting polymer; and (iii)chlorination/bromination of the ion-conducting polymer backbone, therebyreducing degradation sites.

Crosslinking methods can provide or enhance peroxide stability.Additionally, various procedures are described in the literature whereinsulfonated polymers can be crosslinked to further enhance the barrierproperties of the ion-conducting polymer. See e.g., U.S. Pat. No.5,795,496; Kerres, et al., “New Ionomers and their Applications in PEMFuel Cells”, ICE, Stuttgart, Germany (1996); and Kerres, et al., J.Membrane Sci. 139:211-225 (1998).

For example, U.S. Pat. No. 5,795,496 describes a method of crosslinkingion-conducting polymers via the SO₃H groups (sulfonic acid groups) toform sulfone crosslinks between polymer chains. This method entailssulfonating the polymer (e.g., PEEK) using concentrated sulfuric acid,casting of a film, then heating the film to a temperature of 120° C.under vacuum. It is the heating step which causes the crosslinking tooccur.

Despite the enhanced barrier properties provided by crosslinking, thecrosslinking procedure results in decreased ionic conductivity, wateradsorbtion and swelling of the polymer. However, adjustments can be madeto the crosslinking procedures employed in order to minimize thesacrifice of ionic conductivity.

The use of additives can also provide or enhance peroxide stability.Polymer additives have been evaluated that can be used as radicalscavengers within the ion-conducting component of the SPEMs of thepresent invention. Examples of these include Irganox 1135 (PrimaryPhenolic Antioxidant, commercially available from Ciba Geigy) and DTTDP(Di(tridecyl) Thiodipropionate, Secondary Antioxidant, commerciallyavailable from Hampshire). In addition, the ion-conducting componentpolymer can be crosslinked via heating to slow membrane degradation.

Chlorination or bromination of the sulfonated polymer (polymericbackbone) also may be used to increase the usable lifetime of theion-conducting polymer. The combination of reduction in active (attack)sites and increased electron withdrawing properties of such reactionsmay be beneficial to slow membrane degration.

Additionally, various methods may be employed to purify theion-conducting material to optimize or enhance its properties andlong-term stability. For example, the ion-conducting material (e.g.,sulfonated PPSU) may be re-dissolved in a solvent (e.g., NMP), andre-precipitated into water or saturated NaCl solution. This isespecially useful in combination with sulfonation methods which producea heterogeneous sulfonated ion-conducting polymer. Specifically, thisprocedure has been shown to effectively remove overly sulfonated ordegraded fractions of ion-conducting polymers.

In one preferred embodiment of the present invention, the ion-conductingmaterial of the SPEM comprises a sulfonated (SO₃H), phosphonated(PO(OH)₂) or carboxylated (COOH) aromatic polymer. For examples ofphosphonates, see Solid State Ionics, 97 (1997), 177-186. For examplesof carboxylated solid polymer electrolytes, see Solid State Ionics,40:41 (1990), 624-627. For example, the ion-conducting material maycomprise a sulfonated derivative of at least one of the above-listedthermoset or thermoplastic aromatic polymers. It may also comprise asulfonated derivative of a polybenzazole or polyaramid polymer.

Though sulfonated polymers are not readily available in industry, thesynthesis of such polymers is well known to the skilled artisan and canbe found in various patents and publications. See for example, U.S. Pat.Nos. 4,413,106, 5,013,765, 4,273,903 and 5,438,082, and Linkous, et al.,J. Polym. Sci., Vol. 86: 1197-1199 (1998).

In an alternate embodiment, the ion-conducting material of the SPEM ofthe present invention comprises a non-aromatic polymer, such as aperfluorinated ionomer. Preferred ionomers include carboxylic,phosphonic or sulfonic acid substituted substituted perfluorinated vinylethers.

Other preferred ion-conducting materials for use in the presentinvention include polystyrene sulfonic acid (PSSA), polytrifluorostyrenesulfonic acid, polyvinyl phosphonic acid (PVPA), polyvinyl carboxylicacid (PVCA) and polyvinyl sulfonic acid (PVSA) polymers, and metal saltsthereof. More preferably, the ion-conducting material comprises asulfonated derivative of a polyphenylsulfone (PPSU), polyethersulfone(PES), polyimide (PI), polyphenylene sulfoxide (PPSO) andpolyphenylenesulfide-sulfone (PPS/SO₂). These polymers and additionalpreferred polymers are listed in Table 7.

In order to facilitate interpenetration of the ion-conducting polymerinto the pores of the polymer substrate, surfactants or surface activeagents having a hydrophobic portion and hydrophilic portion may beutilized in promoting the interpenetration of the ion-conducting polymerinto the pores of the polymer substrate. These agents are well known inthe art and include Triton X-100 (commercially available from Rohm &Haas of Philadelphia, Pa.).

Compatibilizers may also be employed in producing composite membranes ofthe present invention. As used herein, “compatibilizers” refer to agentsthat aid in the blendability of two or more polymers that wouldotherwise be resistant to such blending. Examples include blockcopolymers containing connecting segments of each component. Theseinclude both potential substrate and/or ion-conducting polymercomponents.

The SPEMs and methods of the present invention will be illustrated byspecific combinations of polymer substrates and ion-conducting polymers.However, the present invention should not be construed as being limitedin use to any particular polymer substrate or ion-conducting material.Rather, the present teachings are suitable for any polymer substrate andion-conducting material meeting the criteria set forth herein.

Several different innovative methods have been developed for producingthe solid polymer electrolyte membranes of the present invention byproviding a polymer substrate interpenetrated with an ion-conductingpolymer. Each method is lower in cost and higher in efficiency thancurrent methods of producing Nafion® (or Nafion®-like) membranes. Thesemethods include imbibing a porous substrate membrane with anion-conducting material, casting a composite membrane from a commonsolvent, sulfonating the pores of a suitable polymer substrate to form acomposite SPEM of the present invention, polymerization of theion-conducting polymer (in-situ) within the pores of the poroussubstrate, and extruding a composite film directly from the mixture of apolymer substrate and ion-conducting material.

The first method uses Nafion® as an example of a suitable ion-exchangematerial, in order to demonstrate the clear advantage of using thecomposite SPEM of the present invention.

Initially, a porous membrane having the desired pore size and porecontent is made using a suitable polymer substrate, e.g., PES or PBO.Either casting or extrusion processes are utilized to produce thesemembranes as described above. The pores of the porous polymer substratemembrane are then interpenetrated with an ion-conducting polymer, e.g.,solubilized Nafion® ion-conducting polymer. The porous membrane is thendried in vacuum to produce a high ionically conducting gel within themicropores and as thin coatings on the surfaces of the compositemembrane. The flexible, pressure-resistant, high Tg, porous substrateprovides puncture and crush-resistance to the thin coating of ionconductor membrane and also to the Nafion®-filled micropores even attemperatures above 175° C. (the Tg of PES is 220° C., PBO has no Tg).

Composite membrane proportions are controlled during the imbibtionprocesses by varying the % wt. of ion-conducting material in solutionproducing a membrane with the target mechanical properties and ionicconductivity.

A comparison of physical chemical properties of Nafion® 117 and SPEMs ofthe present invention follows in Table 1 below.

TABLE 1 SPEMS OF THE PRESENT PROPERTY NAFION ® 117 INVENTION Thickness(mil) - wet 6 to 8 ˜0.1 to ˜5.0, preferably <˜1 mil H+ resistance(ohm-cm) 10.0 ˜5.0 to 100.0, preferably <˜10.0 Tensile (psi) at break2500 to 2700 ˜2500 to ˜50,000, preferably >˜10,000 Elongation (%) atbreak 110 to 130 ˜5 to ˜20, preferably <˜15 % water content* (based on35 to 40 ˜20 to ˜100, dry weight of membrane) preferably <˜50Ion-exchange capacity 0.8 to 1.0 ˜0.2 to ˜2.0, (meq/g dry SPE)preferably ˜1.5 to ˜2.0 Methanol permeability (mA/cm² 50-200 preferably<<˜50 of equivalent current density at 0.5 V) H₂ permeability 600 ˜60 to˜600, (cm³-mil/ft²hr-atm) preferably <˜600 O₂ permeability 330 ˜30 to˜330, (cm³-mil/ft² hr-atm) preferably <˜330 Hydrodynamic H₂O 50 ˜5 to˜50, permeability preferably <˜50 (cm³-mil/ft ²hr-atm) Electro-osmoticH₂O permability 7.5 × 10⁻⁴ 7.5 × 10⁻⁴ (cm³-coulomb) Minimum temperature(° C.) of ˜100 ˜100 to ˜175, thermal/hydrolytic stability preferably˜150 In plane dimensional stability: <20% 0 to ˜20%, dry to wetexpansion of preferably <˜20% membrane Ionomer degradation: <10% 0 to˜20%, (accelerated life testing) preferably <˜10% Chemical stability:20,000 ˜250 to ˜5000 oxidation and hydrolysis (useful life, hours)Crease/crack Pass Pass (ability to withstand five folds in hydrated ordry state) Tear strength Pass Pass (ability to withstand tearing inhydrated or dry state) *Membrane hydrated by soaking in 100° C. H₂O for1 hour

In one preferred embodiment, the substrate polymer is dissolved in anappropriate water-miscible solvent to a predetermined concentration. Thewt. % solution of polymer substrate is selected to produce a film withhigh pore volume (preferably >80%). The polymer substrate solution isthen cast onto glass plates. Immersion of the plates in water coagulatesthe polymer and leaches out the solvent forming the microporoussubstrate membrane in a water swollen state. Nafion® (or otherion-conducting polymers) can then be introduced into the microporousvoids of the substrate membrane using solvent exchange processes to formthe composite membrane. Alternatively, the membrane can be dried firstand then infiltrated with Nafion® solution using vacuum to remove airbubbles and fill the pores with Nafion®. The membrane may also beproduced by an extrusion process as described herein.

In a second preferred embodiment of the invention, porous polymersubstrate membranes containing an ion-conducting material can also beproduced by casting the membranes from a common solution containingappropriate concentrations of the polymer substrate and ion-conductingmaterial. Determination of % wt. ion conductor/% wt. substrate are basedon the desired final thickness, % volume of ion-conducting polymer andthe particular polymers employed. In some instances, this process mayproduce composite membranes in which the ion-conducting polymer domainsizes are smaller and more uniform than in composite membranes producedby imbibing pre-formed porous substrate membranes. In this process, poresize and content can be more easily controlled in the membrane byadjustment of individual component concentrations. The % wt. of thesolution is adjusted to obtain the desired composite. In one embodiment,the ion-conducting polymer solution can be prepared by dissolving theion-conducting polymer in alcohol/water mixtures (e.g., Nafion 2100 EWsolution, 5% from Dupont).

Preferred cosolvents include, but are not limited to, the following:tetrahydrofuran (THF), dimethylacetamide (DMAc), dimethylformamide(DMF), dimethylsulfoxide (DMSO), N-Methyl-2-pyrrolidinone (NMP),sulfuric acid, phosphoric acid, chlorosulfonic acid, polyphosphoric acid(PPA) and methanesulfonic acid (MSA). PPA and/or MSA are preferredsolvents for a polymer substrate and ion-conducting material combinationof PBO/PPSU.

In a third preferred embodiment of this invention, a polymer substrateis chemically sulfonated to produce a sulfonated composite in situ. Thisconcept draws on a number of technologies. A variety of methods existfor the fabrication of porous polymer films, most centered arounddissolving a polymer within a water miscible solvent. A freshly castfilm is then soaked in water causing the polymer to precipitate fromsolution. This phase separation of the solvent and the polymer causesthe formation of the porous network as the solvent is leached into thewater. One example would be the formation of the PBO polymer substrate,but this can be extended to a large number of polymers. One typicalmethod for sulfonating polymers is direct exposure to concentratedsulfuric acid (esp. at elevated temperatures). Imbibing a sulfuric acidsolution into the porous polymer network, followed by rapid heating tohigh temperatures (250-350° C.) has been used to sulfonate somepolymeric systems. If a dilute acid solution is used, the polymer willnot dissolve in the sulfonating process. As a result, only the surfacewithin the porous network will be sulfonated. The product is a compositestructure of unsulfonated polymer with sulfonated polymer on thesurface.

In a fourth preferred embodiment, a method for producing a compositemembrane of the present invention comprises the steps of preparing thesubstrate polymer and subsequently impregnating the substrate withappropriate monomers which are then polymerized in-situ to form thecomposite SPEM.

This concept also draws on a number of well known interpenetratingnetwork (IPN) technologies. See e.g., IPNs Around the World, 1997, JohnWiley & Sons. The porous substrate polymer can be produced as describedin the third preferred embodiment above. Alternatively, a preformedporous substrate with the desired properties can be purchased fromindustry (i.e., Osmonics, Gelman, Memtec, Pall Filtron). For example,Memtec offers a highly asymmetric polysulfone membrane. The preformedsubstrate can then be imbibed with monomers required to synthesizeion-conducting polymers within the pores of the substrate. Of course,the substrate material must be chemically and thermally stable to thepolymerization solvents and/or reaction conditions. Once polymerized, anIPN membrane is created that has properties in accordance with thecomposite SPEMs of the present invention. Further, crosslinking may beused to control swelling in the SPEM as required.

In a fifth preferred embodiment, a solid polymer electrolyte compositemembrane of the present invention can be made by preparing a mixture ofa polymer substrate and an ion-conducting polymer and extruding orcasting a composite film directly from this mixture.

One way to realize the direct extrusion of a solid polymer electrolytecomposite membrane without imbibing a porous polymer substrate with anion-conducting polymer solution would be the fine dispersion of onecomponent in a solution of the other. Provided the solvent used wouldonly dissolve one of the components, a composite could be obtained byextruding or casting this physical mixture of the components followed byremoval of the solvent.

Another possibility would be the dissolution of both components in acommon solvent. A composite membrane would be formed with the phaseseparation of the components, either before or after the removal of thesolvent. Similarly, many polymers can be uniformly blended in the melt(e.g. without solvent). However, upon cooling the components may phaseseparate into the appropriate interpenetrating network (IPN)-typestructure. This last method would also be useful from the standpointthat no solvent is required.

Examples of these methods include blending of sulfonated andunsulfonated versions of one polymer in the high temperature melt,followed by their phase separation on cooling. The typical solution ofPBO in polyphosphoric acid would dissolve the ion-conducting polymer.Fibers of a suitable polymer substrate could be dispersed into asolution (or melt) of the ion-conducting polymer. Extrusion or castingof this mixture, followed by removal of the solvent would provide atypical fiber reinforced composite structure.

Optimal interpenetration of the polymer substrate by the ion-conductingpolymer is estimated to be in the range of 40-90% volume. Morepreferably, interpenetration is in the range of 70-80% volume. Percentvalues can be determined by comparing the thickness of a membraneinfiltrated with ion-conducting polymer with a control membrane with noinfiltration. For example, a doubling in thickness would indicate 50%interpenetration.

The following tables further illustrate SPEMs of the present invention.

TABLE 2 Comparative Data for Water and Methanol Transmission ExperimentsFilm: Avg. Avg. Avg. Film: 1 HR WVTR WVTR MeOHTR 2 HR Boiling (25° C.)(80° C.) (25° C.) Water Water g/(mil* g/(mil* g/(mil* SAMPLE: UptakeUptake 100 in² 100 in² 100 in² Material & Type (%) (%) *24 hr) *24 hr)*24 hr) Unsulfonated 0.00 1.20 5.7 106.0 NT Udel PES 50% Sulfonated 8.703.23 47.3 673.0 NT Udel PES (FMI) 75% Sulfonated 12.12 11.94 29.1 814.4NT Udel PES (FMI) 85% Sulfonated 12.50 92.70 116.2 2850.0 NT Udel PES(FMI) 100% Sulfonated 1074.68 462.25 109.30 3095.3 288.1 Udel PES (FMI)in PBO Nafion ® 117 16.88 35.34 1003.10 15200.4 2680.1 Control PBOControl 0.00 0.30 0.0 4.1 NT NT = Not Tested

The following table shows comparative data for membrane properties forPBO/sulfonated PES (75%) and PBO/sulfonated PES (85%) and Nafion®.

TABLE 3 Comparative Data of Membrane Properties MEMBRANE PBO/ PBO/sulfonated PES sulfonated PES Nafion ® Property (75%) (85%) 117Thickness (mils) 1.5 1.5 7.0 Water content (%) 45 55 35-40 IEC_(dry)(meq/g) 0.55 0.96 0.91

The following tables show corresponding structures for certain polymersreferred to in the specification.

TABLE 4 Nafion ®

PBO (poly(bisbenzoxazole-1,4- phenylene)

PBT (poly(benzo(bis-thiazole)- 1,4-phenylene))

PBI (poly(benzo(bis-diazole)-1,4- phenylene)

PAR (polyaramid or Kevlar ®)

PPSO₂ (polyphenylene sulfone)

TABLE 5 PSU (polysulfone) (Udel ®)

PES (polyether sulfone)

PEES (polyether-ether sulfone)

PAS (polyarylether sulfone) or PPSU (polyphenyl sulfone)

TABLE 6 PI (polyimide) or poly(pyromellitic dianydride/ para phenylenediamine)

PPO (poly(2,6 dimethyl 1,4 phenylene oxide))

PPSO (polyphenylene sulfoxide)

PPS (polyphenylene sulfide)

PPS/SO₂ (polyphenylenesulfide sulfone)

PPP (polyparaphenylene)

PPQ (poly(phenylquinoxaline))

PEK (polyetherketone)

PEEK (polyetheretherketone)

PEKK (polyetherketoneketone)

PEEKK (polyetheretherketone ketone)

PEKEKK (polyetherketone- etherketone-ketone)

TABLE 7 PEI (polyetherimide) R = aryl, alkyl, aryl ether or alkylether

Polysulfone (Udel ®)

Polyphenylsulfone (Radel R ®)

Polyethersulfone (Radel A ®)

and

Polyether sulfone (Ultrason E ®)

Poly(hexafluoroisopropylidine dianhydride/meta phenylene diamine)

Poly(triphenylphosphine oxide sulfide-phenylsulfone-sulfide)

Poly(2-phenylsulfide-1,4- phenylene)

Poly(hexafluoroisopropylidene dianhydride/diaminodiphenyl sulfone)

(PVSA) polyvinyl sulfonic acid

Poly(hexafluoroisopropylidene dianhydride/ diaminodiphenoxybenzene)

Poly-X ® (Maxdem)

Poly(pyrolmellitic diimide-1,3- phenylene)

Poly(diphthalimide-1,3- phenylene)

(PPO) poly(1,4-phenylene oxide

Diphenyl PPO (poly(2,6- diphenyl-1,4-phenylene oxide)

PBPS (poly(benzophenone sulfide))

Poly(benzophenone sulfide- phenylsulfone-sulfide)

Poly(vinyl carboxylic acid)

Poly(trifluorostyrene sulfonic acid)

Poly(vinyl phosphonic acid)

Poly(styrene sulfonic acid) (PSSA)

TABLE 8 1 M Me(OH) Permeability (× 10⁻⁶) Dim. Thickness % Dry Vol WaterMoles CO₂ Stability Serial ICP (mils) ICP IEC Content ResistancePeroxide per min per (% Area Number ICP Type (ID) (% wt) Dry Wet(Estimated) (meq./g) (%) (ohm*cm²) Test cm² per mil Change) Nafion 117Nafion 117 (1100 EW) 100 7.1 8.7 100  0.90 38 0.203 −3.2% 1.74  ˜20%Control FMI 539-22- 75% SPSU (Udel) ˜30 NT 1.5 49 0.55 45 NT NT NT NT 1FMI 539-22- 75% SPSU (Udel) ˜30 NT 1.5 49 0.96 55 NT NT NT NT 2 FMI539-22- 100% SPSU (Udel) ˜30 NT 2.0 49 NT NT NT NT 0.187 NT 3 FMI 126-75% SPECS (Ultrason 12 2.0 3.1 29 0.23 27 127.0 −38% NT NT 08E E) FMI126-08F 75% SPES (Ultrason 8 1.65 1.8 19 0.07 30 2177.1 −36% NT NT E)FMI 126- 1100 EW (DuPont) 10 0.8 0.9 16 0.29 43 1290.8 NT NT nil 16N FMI126- 1100 EW (DuPont) 10 0.9 1.0 16 0.39 32 1183.2 NT NT nil 16O FMI126-17P 150% SPPSU (Radel 20 1.1 3.5 40 0.82 87 5.11 NT NT nil R) FMI126- 100% SPPSU (Radel 20 1.2 2.5 40 0.62 60 16.60 NT 0.073 nil 17Q R)FMI 126-18T 150% SPPSU (Radel 20 2.1 4.7 40 0.54 90 1.85 −63% NT nil R)FMI 126- 100% SPPSU 20 3.1 3.7 40 0.50 92 16.34 −56% 0.179 nil 18U(Radel R) RMI 126- 200% SPPSU 20 1.2 2.0 94 1.66 138  0.292 NT NT nilAY1 (Radel R) FMI 126- 1100 EW (Dupont) ˜17 2.0 2.5 40 1.16 47 0.637 NTNT nil 79BB FMI 126- 200% SPPSU 20 1.0 1.5 94 0.91 143  0.140 NT 0.261nil 82BE (Radel R) RMI 126- 200% SPPSU 8 1.1 2.0 79 1.13 64 0.263 NT NTnil d91BO (Radel R) NT = NOT TESTED

EXAMPLES OF THE INVENTION

The polymers described herein are commercially available from a varietyof suppliers (unless otherwise indicated). Suppliers of these polymersinclude the following: RTP, Ticona, Alpha Precision, Polymer Corp.,Amoco Polymers, Greene Tweed, LNP, Victrex USA, GE Plastics, NortonPerformance, BASF, Mitsui Toatsu, Shell, Ashley, Albis, PhillipsChemical, Sumitomo Bake, Sundyong, Ferro, Westlake, M.A. Hanna Eng.

The following procedures were employed in the fabrication and testing ofsamples that were prepared in accordance with the membranes and methodsof this invention.

General Procedures

IEC PROCEDURE

1. Cut out pieces of sulfonated films (target weight 0.2 g, target filmthickness 2 mils).

2. Vacuum dry films at 60° C., record dry weights and note if films arein H+ or Na+ form.

3. Boil deionized water in separate beakers on hotplate.

4. Place films into boiling water.

5. Boil films vigorously for ½ hour.

6. Prepare 1.5N H₂SO₄.

7. Place films into H₂SO₄ and soak for ½ hour.

8. Remove films and rinse with deionized water.

9. Boil in deionized water again. Repeat until the films have soaked inH₂SO₄ three times.

10. Remove films from boiling water, pat film surface with paper towel,and rinse carefully with deionized water.

11. Place films in another beaker of water and check for pH.

12. Continue to rinse the films with water until pH is neutral to removeany excess acid trapped in the folds of the film.

13. Prepare saturated NaCl solution.

14. Boil the NaCl solution, pour into screw cap vials, add film and cap.

15. Place capped vials with film into water bath at 90° C. for 3 hours.

16. Remove capped beaker from water bath and cool to room temperature.

17. Remove the films from NaCl solution by pouring the salt solutioninto another beaker (save), wash the films with deionized water (saveall washings—they will be used for titration).

18. Titrate the NaCl solution with 0.1N NaOH.

19. Take the films, pat with paper towel and take wet weight. (Use wetweight to determine water content of films.)

20. Dry the films under vacuum at 60° C. until constant weight.

21. Take dry weight and use this to calculate IEC.

PEROXIDE TEST PROCEDURE

22. Place films into the H+ form by following steps 1-12.

23. Make peroxide solution by adding 4 ppm Fe to 3% hydrogen peroxide(28.5 mg of ammonium iron (II) sulfate hexahydrate per liter of peroxideobtained from Aldrich).

24. Place the peroxide solution into water bath at 68° C.

25. Add films to the peroxide solution already at 68° C.

26. Peroxide test for 8 hours and record film properties (mechanical,color, handling etc.).

27. If film passes, remove from peroxide, rinse with water to remove alltraces of peroxide solution.

28. Follow steps 13-21 to obtain post-peroxide test IEC.

CROSSLINKING PROCEDURES

Ion-conducting polymeric samples can be crosslinked in the acid (H+)form to improve ICP stability. Normally, crosslinking is performed invacuum, to exclude oxygen from the system (which can cause ICPcharring). The vacuum oven should be preheated to temperatures of atleast about 200° C. The ICP sample is then heated in the vacuum oven fora prolonged period of time. The ICP sample should be tested before andafter crosslinking for IEC and peroxide stability in order to evaluatelong term membrane stability. See e.g., Example 15 below.

FILM FABRICATION PROCEDURES

Film Casting:

Unoriented, microporous substrate films can be made by dissolving thepolymer in a suitable water miscible solvent and casting onto a glassplate or other surface. For example, dry PBO polymer can be dissolved inmethanesulfonic acid (MSA). The films are slowly placed into a waterbath, where solvent is rinsed from the films forming microporous,water-swollen membranes of PBO polymer. Subsequent washing allows forremoval of all traces of the solvent.

Extrusion:

In general, the extrusion of a polymer solution (in a water misciblesolvent) followed by its coagulation and washing in a water bath allowsthe formation of microporous polymer films. The mechanical propertiesand porosity are controlled by the characteristics of the polymersolution and the details of the extrusion process.

Microporous, biaxially-oriented films of liquid crystal polymers (LCPs)can be produced using a counter-rotating die (CRD) extrusion process.Solutions of the polymer are extruded using two annular and concentricmandrels that rotate in opposite directions. The rotation of themandrels creates a transverse shear flow that is superimposed on theaxial shear developed as the polymer solution is extruded through thedie. The angle that the LCP fibrils make with the longitudinal axis ofthe tubular extrudate is ±θ, where θ can be varied from near-zero toabout 65 degrees. The die rotation presets the biaxial (±θ) orientationof the emerging extrudate. Subsequent post-die blowout (radialexpansion) and draw (extrusion direction stretching) are used to furtheradjust and enhance the biaxial orientation.

The tubular extrudate leaving the die is expanded radially (blown) withpressurized nitrogen and stretched in the machine direction by pinchrolls to achieve the desired film thickness. The blown and drawn PBObubble is immediately quenched in a water bath where the film structureis coagulated, or “locked-in-place”, and the polyphosphoric acid ishydrolyzed into phosphoric acid. The PBO film is collected under wateron a spool, which is later transferred to a fresh water storage tankwhere it is thoroughly rinsed and stored in the water-swollen stateuntil needed.

See e.g., U.S. Pat. No. 4,963,428.

Solvent Exchange:

The water swollen microporous substrate is used to complete a staged“solvent” exchange. The initial solvent (100% water) is exchanged forthe desired solvent (e.g. NMP, alcohol, etc.) in a number of stages. Tominimize the collapse of the pores, the exposure of the substrate filmto the air is minimized. For example, note the 5 part exchange fromwater to NMP as follows:

START FINISH Exchange #1: 100% Water 75% Water/25% NMP Exchange #2: 75%Water/25% NMP 50% Water/50% NMP Exchange #3: 50% Water/50% NMP 25%Water/75% NNP Exchange #4: 20% Water/80% NMP 100% NMP Exchange #5: 100%NMP Fresh (anhydrous) NMP

Microporous substrate films are stored in the exchanged solvent untilthey are used in composite SPEM formation.

SULFONATION PROCEDURES

Sulfonation Procedure I:

Aromatic PES polymers can be sulfonated to controlled degrees ofsubstitution with sulfonating agents. The degree of substitution iscontrolled by the choice of and mole ratio of sulfonating agent toaromatic rings of the polymer, by the reaction temperature and by thetime of the reaction. This procedure offers a method for carrying outsulfonation in a heterogeneous manner, i.e., sulfonation of precipitatedpolymer crystals.

The polymer (preferably a polyethersulfone) is first dissolved in theappropriate solvent (preferably methylene chloride) and then allowed toprecipitate into a fine crystalline suspension. Sulfonation is carriedout by simple admixture of the suspension with a sulfonating agent.Suitable agents include chorosulfonic acid and, preferably, sulfurtrioxide (Allied chemicals stabilized Sulfan B® in CH₂Cl₂). Thesulfonating agent used should be in sufficient proportion to introduce anumber of sulfonate groups onto the polymer that is within the range ofbetween 0.4:1 to 5:1 per polymer repeat unit, although this is notcritical. The temperature at which sulfonation takes place is criticalto limiting the side reactions but varies with the type of polymer (apreferable temperature is within the range of from −50° to 80° C.,preferably −10° to +25° C.).

When the desired degree of sulfonation has been reached, the sulfonatedpolymer may be separated from the reaction mixture by conventionaltechniques such as by filtration, washing and drying.

The polymer products of the process of the invention may be neutralizedwith the addition of a base, such as sodium bicarbonate, when desiredand converted to the alkali salts thereof. The alkali salts of thepolymer products of the invention may be used for the same purposes asthe parent acid polymers.

See e.g., U.S. Pat. No. 4,413,106.

Sulfonation Procedure II:

Concentrated sulfuric acid is used as the solvent in this procedure. Thecontent of the sulfonating agent, sulfur trioxide, is based on the totalamount of pure (100% anhydrous) sulfuric acid present in the reactionmixture, and is kept to a value of less than 6% by weight throughout theentire sulfonation. The sulfur trioxide may be mixed in dissolved form(oleum, fuming sulfuric acid) with concentrated sulfuric acid. Theconcentration of the starting sulfuric acid and oleum were determined bymeasuring their density immediately before use in the reactions.

The temperature of the reaction mixture is kept at less than +30° C.throughout the reaction. The sulfonation procedure is stopped by pouringthe reaction mixture into water.

More specifically, the polymer is first dried in high vacuum at roomtemperature to constant weight, then dissolved in concentrated sulfuricacid. Oleum is then added drop-wise over a period of hours with constantcooling below +30° C., and with stirring. When all of the oleum has beenadded, the reaction mixture is stirred for a further period of hours atthe same temperature. The resultant viscous solution is then run intowater and the precipitated polymer is filtered off. The polymer is thenwashed with water until the washings no longer are acidic, and it isthen dried.

If these conditions are maintained, a controllable sulfonation ofaromatic polyether sulfones is possible and polymer degradation can besubstantially or completely prevented.

Though less preferred, another variation of this procedure is to add thesulfur trioxide either in pure solid state or in gaseous state to asolution of the polymer in concentrated sulfuric acid.

See e.g., U.S. Pat. No. 5,013,765.

Sulfonation Procedure III:

This sulfonation procedure is directly analogous to procedure I,however, the polymer remains in solution at least until the addition ofthe sulfonating agent.

Polymer is first dissolved in a solvent that is compatible with thesulfonating agent (e.g. methylene chloride) in a nitrogen atmosphere.The sulfonating agent is added to this solution over the course ofseveral hours. The resulting solution or suspension (if the polymerprecipitates as the reaction occurs) is allowed to react, again forseveral hours.

When the desired degree of sulfonation has been reached, the sulfonatedpolymer may be separated from the reaction mixture by conventionaltechniques such as by filtration, washing and drying. If the sulfonatedpolymer remains in solution, the solvent can be removed simply byevaporation or precipitation into a non-solvent.

MEMBRANE PREPARATION

Microporous substrate films previously exchanged into the appropriatesolvent are placed consecutively into solutions of the variousion-conducting polymers (ICP) with increasing concentration (in the samesolvent as the unfilled microporous substrate). This technique is knownin the art (see, e.g., U.S. Pat. No. 5,501,831). Generally the use ofsmaller changes in ICP concentration seems to allow the formation ofcomposite films with higher final ICP loadings. In the case of moreviscous polymer solutions, the microporous substrates and the imbibingsolution are heated (up to 100° C.). Once imbibed with the ICP, thecomposite film is placed between 6″ diameter tension rings. As the ringsare bolted together, the composite is carefully stretched to eliminateany veins or defects in the substrate. Once the rings are completelybolted together, the setup is left to air dry (e.g. in the hood)overnight. This will usually remove much of the excess ion-conductingpolymer's solvent by evaporation.

The films are further dried by one of two methods. For low boilingsolvents the composite films are heated under vacuum with pressure(about 100 psi) to prevent blistering of the films. In these instancesporous, Teflon® coated shims are used to allow the solvent vapor toescape. Higher boiling composite films are simply heated under vacuumpast the boiling point of the solvent. The overall uniformity of thefinal composite membrane can be improved by further pressing thesecomposites at elevated temperature and pressure.

COMPOSITE MEMBRANE TESTING METHODS

IEC. % Water Content, Membrane Degradation:

During this procedure, films are immersed in distilled H₂O and boiledfor a period of 30 minutes. The films are then placed in a solution of1.5N H₂SO₄ at room temperature and soaked for a period of 30 minutes.This is repeated three separate times to ensure proper H+ ion exchangeinto the membrane. Films are rinsed free of acid (pH of rinsewater >5.0) and placed into separate beakers, each filled with asaturated solution of NaCl. The salt solution is boiled for a period ofthree hours. The films, which are now in the Na+ form, are removed fromthe salt solution, rinsed with distilled water and padded to removeexcess water. Now a wet weight and thickness of the sample are measured.While in the Na+ form, the films are dried in an air oven at atemperature of 60° C. The dry weight and thickness of the films aremeasured and the percent water content is calculated. The salt solutionsare titrated with 0.1N NaOH to a phenolphthalein endpoint and IEC dry(meq/g) values calculated.

Ionic Conductivity:

Transverse ionic conductivity measurements are performed on film samplesin order to determine the specific resistance (ohm*cm²). Prior to theionic conductivity measurements, film samples are exchanged into the H+form using the standard procedure discussed above. To measure the ionicconductivity, the film samples are placed in a die consisting ofplatinum-plated niobium plates. The sample size tested is 25 cm². Priorto assembling in the measuring device, platinum black electrodes areplaced on each side of the film sample to form a membrane-electrodeassembly (MEA). To insure

complete contact during the resistivity measurement, the MEA iscompressed at 100 to 500 psi. The resistance of each film is determinedwith a 1000 Hz, low current (1 to 5 A) bridge, four point proberesistance measuring device and converted to conductivity by usingformula 1.

(1)C=t/RxA

Where:

C=Conductivity (S/cm)

R=Sample Resistance (ohm)

t=Wet sample thickness (cm)

A=Sample area (cm2)

Measurements are converted to specific resistance by calculating theratio of thickness over conductivity (ohm*cm²).

Membrane Degradation:

Accelerated degradation testing is carried out using 3% H₂O₂ solutionwith 4 ppm Fe++ added as an accelerator. The films are tested for aperiod of 8 hours at a temperature of 68° C. The percent degradation ofIEC was measured in the film samples after the test. After 8 hours, thefilms are removed from solution, and re-exchanged using 1.5 N H₂SO₄. TheIEC is recalculated, and the test result expressed as the % loss in IEC.This test simulates long term (several thousand hours) of actual fuelcell operation. For H₂/O₂, fuel cells, <10% IEC degradation in this testwould be considered acceptable.

EXAMPLE 1 Sulfonation of Radel R® Using Sulfan B® (100% and 150%Stoichiometric Sulfonation)

Sulfonation Procedure I was used in the following example.

Two separate 1000 ml 3 neck resin kettles (with ribs) equipped with anN₂ inlet, addition funnel, and overhead stirrer were charged with thefollowing reactants: 340 ml of dichloromethane and 50.00 grams of RadelR® Polyphenylsulfone Polymer (beads). These mixtures were stirred untilsolutions formed (approximately 0.25 hours). Once solutions formed, theywere cooled in ice baths to about a temperature of 0° C. (ice bath wasmaintained throughout the duration of the addition and reaction). (Notethat Radel R® was dried at 70° C. under full dynamic vacuum for about 12hours to remove any adsorbed moisture.)

While the above solutions were cooling, the following amounts of SulfanB® were combined with dichloromethane in two separate 125 ml additionfunnels. In funnel #1 (100% sulfonation) 10.00 grams of Sulfan B® wascombined with 120 ml of dichloromethane. In funnel #2 (150% sulfonation)15.00 grams of Sulfan B® was combined with 120 ml of dichloromethane.

As polymer solutions were cooled, the polymer precipitated from solutionto form a viscous paste. To each of these polymers approximately 350 mlof dichloromethane was added to aid in the uniform mixing of thesuspensions. The diluted suspensions were then cooled to ice bathtemperatures once again.

To the rapidly stirring cooled and diluted polymer suspension, theSulfan B® solutions were added drop-wise over a period of 3.5 to 4.0hours.

Upon completing the addition of the Sulfan B®/dichloromethane solution,the reaction mixtures were permitted to stir at ice bath temperaturesfor another 2.5 hours, then the reaction was stopped by addingapproximately 10 ml of deionized water to each of the reaction mixtures.

The reaction mixtures (white dispersions) were recovered by filtrationusing a glass frit. Products (white powder) were washed 3× with 100 mlportions of dichloromethane. The washed products were then permitted toair dry in the hood. 20% solutions of the dried products were made inNMP and cast on soda lime glass plates. The freshly cast films were leftto stand in a dry box with a relative humidity of less than 5% for aperiod of 24 hours. The cast films were heated at 70° C. under fulldynamic vacuum for an hour prior to floating the films off withdeionized water. The floated films were then permitted to air dryovernight.

The 100% and 150% sulfonated products swell greatly in water and becomeopaque, but when films are dry they shrink and become clear once again.The mechanical strength of these films allows creasing while resistingtearing. Films of the 100% and 150% products are not soluble in boilingwater, and under these conditions also maintain their mechanicalproperties.

IEC:

100% sulfonated Radel R® unpurified=1.39 meq./g

150% sulfonated Radel R® unpurified=1.58 meq./g

These polymers were further purified by dissolving in NMP (at 20wt. %)and then precipitated into a large excess of saturated salt water. Theresulting polymers were soaked in sodium bicarbonate, washed severaltimes with water, then dried under vacuum (˜100° C.). These polymerswere also cast into films as described above for characterization.

IEC:

100% sulfonated Radel R® purified=1.26 meq./g

150% sulfonated Radel R® purified=1.44 meq./g

Water Pick-up (wt. %):

100% sulfonated Radel R® purified=56%

150% sulfonated Radel R® purified=110%

EXAMPLE 2 Sulfonation of Radel R® Using Sulfan B® at 200% StoichiometricSulfonation

Procedure:

This sulfonation reaction was run very similarly to those previouslydescribed in Example 1 (100, 150% sulfonations with Sulfan B®), withminor adjustments, which are noted below:

After the precipitation of the polymer from the initial dichloromethanesolutions, only 200 ml of new solvent was added to enhance stirring (inExample 1, an additional 350 ml was used).

Previous data suggests that not all of the SO₃ reacts with the polymerover 6 hours at 0-5° C. Therefore, one reaction was carried out at icebath temperatures for 8 (or more) hours and then allowed to warm to roomtemperature. Although the resulting sulfonated Radel R® was darker incolor than the batch that was quenched after only 6 hours, the polymerwas still water insoluble and showed good film properties. Theproperties of such ICPs are:

200% Sulfonated Radel R (quenched after 6 hrs at 0-5° C.): IEC=1.67meq/g, Water Pick-up=144%, Conductivity=0.073 S/cm.

200% Sulfonated Radel R (quenched after allowed to warm up): IEC=1.90meq/g, Water Pick-up=174%, Conductivity=0.091 S/cm

A similar reaction was carried out in which the SO₃ was allowed to reactlonger, but was kept cold (0-5° C.) throughout the reaction. The productisolated from this reaction had an IEC value (1.71 meg/g) which wasbetween the two batches described above.

Note: Percent sulfonation in terms of stoichiometry, e.g., 200%sulfonation, refers to the use of a particular excess per each polymericrepeat unit, e.g., two moles in the case of 200% sulfonation.

EXAMPLE 3 Sulfonation of BASF Ultrason® Polyether Sulfone Using SulfanB® (85%, 75%, and 65% Sulfonation)

Sulfonation Procedure III was used in the following example.

Three separate 1000 ml 3 neck resin kettle (with ribs) equipped with anN₂ inlet, addition funnel, and overhead stirrer were charged with thefollowing reactants: the first resin kettle was charged with 350 ml ofdichloromethane and 51.00 grams of BASF Ultrason polyether sulfonepolymer (fine powder), the second was charged with double the amount ofreactants, and the third was charged with the same ratios as the first.Ultrason was dried at 70° C. under dynamic vacuum for about 12 hoursprior to use. These mixtures were stirred until solutions formed(approximately 15 min.). Once solutions formed, they were cooled in icebaths to about a temperature of 0° C. (ice bath was maintainedthroughout the duration of the addition and reaction).

While the above solutions were cooling, the following amounts of SulfanB® were combined with dichloromethane in three separate 125 ml additionfunnels. In funnel # 1 (85% sulfonation) 14.94 grams of Sulfan B® werecombined with 120 ml of dichloromethane. In addition funnel #2 (75%sulfonation) 26.32 grams of Sulfan B® were combined with 120 ml ofdichloromethane. In addition funnel #3 (65% sulfonation) 11.80 grams ofSulfan B® were combined with 120 ml of dichloromethane. These solutionswere then added dropwise to the corresponding rapidly stirring cooledpolymer solutions over a period of 4 hours.

Addition of the Sulfan B® solution caused the polymer to precipitate andform a very viscous sludge. These were diluted with the followingamounts of anhydrous dichloromethane. Reaction # 1 was diluted with 70ml of anhydrous dichloromethane, #2 was diluted with 600 ml ofdichloromethane, and #3 was diluted with 400 ml of dichloromethane. Uponcompleting the addition of the Sulfan B®/dichloromethane solution, thereaction mixture was permitted to stir and warm to room temperatureovernight. The following morning the reaction mixtures (a whitedispersion) were filtered using a glass frit. Products (a fine whitepowder) were washed 3× with 100 ml. portions of dichloromethane. Thewashed products were then permitted to air dry in the hood for 4 hours.

20wt. % solutions of the dried products were made in NMP. The polymersolutions were filtered using a 2.5 micron glass fiber filter cartridge.The filtered products were then precipitated into approximately 4 litersof water. These products were then washed 2× with deionized water. Thewashed products were converted into the sodium form by soaking in a 2.5%sodium hydroxide solution over several days. These were then washed withdeionized water until a neutral pH was achieved. Finally, the sampleswere thoroughly dried in vacuum.

When 85% sulfonated polymer is boiled in water, it swells greatly andpartially dissolves. The 75% and 65% sulfonated products do not dissolvein boiling water, however they showed considerable swelling.

IEC:

65% sulfonated Ultrason purified=0.69 meq./g

75% sulfonated Ultrason purified=0.80 meq./g

85% sulfonated Ultrason purified=1.08 meq./g

Water Pick-up (wt. %):

65% sulfonated Ultrason purified=18%

75% sulfonated Ultrason purified=21%

EXAMPLE 4 Synthesis of Sulfonated Udel® Polyether Sulfone UsingChlorosulfonic Acid (33-100% sulfonation)

Sulfonation Procedure III was used in the following example.

Procedure:

A 1000 ml. 3 neck round bottom flask equipped with a condenser, N₂inlet, and overhead stirrer; was charged with 175 ml of dichloromethaneand 50.0 grams of Udel® Polyethersulfone. This mixture was stirred untila solution formed (approximately 3 hours).

While the above was stirring 11.49 grams of chlorosulfonic acid wasmixed with 50 ml. of dichloromethane in a 125 ml. addition funnel. Thissolution was added dropwise to the rapidly stirring polymer solutionover a period of an hour. The reaction mixture changed from a clearamber color to a cloudy caramel color. Upon completing the addition theacid solution, the reaction mixture was permitted to stir at roomtemperature over night.

After stirring at room temperature for 28 hours the reaction mixture washeated in a water bath until a mild reflux was achieved, and it was keptrefluxing under these conditions for an hour. After heating the reactionmixture for an hour the heat source was removed and the mixture waspermitted to cool.

After removal of the solvent, the product was dissolved in THF. Filmscast from this solution were transparent and creasible. IR spectra andwater absorption were consistent with the formation of sulfonated Udel®Polyethersulfone.

Complete reaction of the chlorosulfonic acid corresponds to the additionof 0.85 sulfonate groups per repeat unit of the polymer (85%).Similarly, sulfonated versions of Udel® Polyethersulfone were made withlevels of sulfonation from 33 to 100%.

IEC:

75% sulfonated Udel=1.10 meq./g

85% sulfonated Udel=1.19 meq./g

Water Pick-up (wt. %):

75% sulfonated Udel=12%

85% sulfonated Udel=93%

EXAMPLE 5 Synthesis of Sulfonated-Polyimides (via Monomers)

Sulfonation procedures described by Sillion [French patent 9,605,707]were used as a guide in the following example. However, alternatemonomers and reaction conditions were employed.

Sulfonated polyimides are produced by the reaction of a sulfonateddiamine with a dianhydride, using a 1.000 molar ratio ofdiamine/dianhydride, in a solvent under an inert atmosphere. An exactdiamine/dianhydride molar ratio of 1.000 is required in order to achievehigh molecular weight polymers. Polyimides are synthesized through anintermediate polyamic acid form which contains an amide linkage andcarboxylic acid groups. This polyamic acid may or may not be isolatedfrom the reaction solution. The polyamic acid is converted to thecorresponding polyimide by a cyclization reaction involving the amidehydrogen and neighboring carboxylic acid groups, forming a five (or six)membered imide ring, with the evolution of water as a reactionbyproduct.

Polyimides can be made via two general procedures: 1) first synthesize,at or below ambient temperatures its solvent-soluble polyamic acid form,then chemically or thermally transform this polyamic acid to thepolyimide; and 2) directly synthesize the solvent-soluble polyimideusing reaction temperatures in excess of 100° C. to distill water fromthe initial reaction solution. Each of these procedures was used atFoster-Miller to produce sulfonated-polyimides. The details of thesereactions are presented below.

Formation of the Sodium Salt of 2,4-Diaminobezenesulfonic Acid(2,4-NaDBS).

2,4-Diaminobenzenesulfonic acid (2,4-DBS) (5.00 grams, 26.6 mmoles) wasdispersed in 95.29 grams anhydrous methanol at ambient temperaturesunder a positive nitrogen atmosphere in a reaction flask equipped with areflux condenser, magnetic spinbar for stirring purposes and pressureequalizing funnel. A cloudy dispersion of sodium hydroxide (1.06 grams,26.6 mmoles) in methanol (93.4 grams) at a concentration of 1.1 wt.percent was placed in the pressure equalizing funnel and added dropwiseto the stirring 2,4-DBS/methanol dispersion at ambient temperatures.Additional methanol (195 grams) was added to transform the dispersioninto a brownish orange colored solution after stirring overnight,containing approximately 1.3 wt. percent solids. Initially, 2,4-DBS wasfound to be insoluble at similar concentrations in methanol, indicating2,4-DBS has been converted into a more soluble material. The solutionwas heated at reflux for several hours to ensure the reaction had goneto completion, cooled to ambient temperatures, and filtered to removeany trace amounts of undissolved material. Hexanes (275 mL) were thenadded to the solution to precipitate a tannish solid. This solid wascollected by filtration, washed with hexanes and air dried. The materialexhibited a single reproducible endothermic absorption between 246° to252° C., with a peak width at half height of 5.3° C. by differentialscanning calorimetry. Its infrared spectrum (IR) showed absorptionstypical for a —NH₂ amine (3426, 3380, and 3333 cm⁻¹), a primary amine(3199 cm⁻¹), aromatic C—Hs (1624 cm⁻¹) and SO₃ salt (1230 and 1029 cm⁻¹)groups. These SO₃ salt absorptions were located at values different thanthose observed for HOSO₂ in 2,4-DBS, which appeared at 1302 and 1134cm⁻¹. The amine absorption at 3426 cm⁻¹ in this material was also notpresent in 2,4-DBS. The IR absorption typical for a sulfonic acid(—SO₂—OH) group at 2609 cm⁻¹ in 2,4-DBS was also absent. The combinationof all this information indicates the tannish solid product is sodium2,4-diaminobenzenesulfonate (2,4-NaDBS).

This material was be used as an alternative to 2,4-DBS in the synthesisof sulfonated polyimides due to its increased thermal stability andpotentially increased reactivity toward polyimide formation (aminegroups in the 2,4-NaDBS are more reactive toward the dianhydride monomerdue to electron release from the sulfonate group).

Synthesis of the Copolyamic Acid Derived from 6FDA, m-Phenylenediamine(m-PDA) and 2,4-NaDBS (6FDA/m-PDA/2,4-NaDBS PAA).

2,4-DBS (7.75 mmoles) and m-PDA (7.75 mmoles) were easily dissolved inanhydrous dimethylsulfoxide (DMSO) at ambient temperatures under anitrogen atmosphere. 6FDA (15.5 mmoles) was added all at once to thediamine solution and the mixture was stirred at ambient temperaturesunder a nitrogen atmosphere. The reaction mixture became warm to thetouch as the 6FDA began to dissolve and the resulting, solution wasstirred overnight at ambient temperatures. This clear reddish brownsolution contained 15.0 wt. percent polymer and exhibited a viscositysimilar to warm syrup, indicating polymers with reasonable molecularweights had been produced. The IR spectrum of the reaction solutionshowed absorptions typical for —NH of an amide (3249 and 3203 cm⁻¹), C=0amide I stretch (1683 cm⁻¹), aromatic C—Hs (1607 cm⁻¹), N—C=0 amide IIsymmetric stretch (1548 cm⁻¹) and SO₃ salt (1256 and 1020 cm⁻¹). The IRabsorption for —OH of HOSO₂ at 2609 cm⁻¹ was absent from the spectrum.This IR data is consistent with the formation of the6FDA/m-PDA/2,4-NaDBS copolyamic acid.

A sample of the polyamic acid solution was cast into a film on a NaClsalt IR disc and the film/disc was heated in a circulating air oven for1 hour each at 100° , 200° and 300° C. to convert the copolyamic acid toits copolyimide form. The IR spectrum of copolyimide film showedabsorptions typical for C=0 imide stretch (1787 and 1733 cm⁻¹), aromaticC—H (1603 cm⁻¹), C—N imide stretch (1362 cm⁻¹), HOSO₂ acid (1298 and1145 cm⁻¹), SO₃ salt (1256 and 1029 cm⁻¹) and polyimide (745 and 721cm⁻¹). IR absorptions typical for polyamic acids at 1683 and 1545 cm⁻¹as well as the —OH of HOSO₂ at 2609 cm⁻¹ were absent. Nevertheless, itappears that some of the NaSO₃ groups were converted to HOSO₂ by freeacid generated during the continuing polymerization.

Thermal Imidization of 6FDA/m-PDA/2,4-NaDBS PAA.

A sample of the reaction solution was cast into a large film with aninitial thickness of 0.007 inch on a glass substrate using a motorizedfilm casting table located inside a low humidity chamber (<10 percentrelative humidity). The resulting clear copolyamic acid film was heatedin a circulating air oven for 1 hour each at 100°, 200°, and 250° C. toform a reddish brown copolyimide film. A final temperature of 250°rather than 300° C. was used to hopefully reduce the thermal degradationof the resulting NaSO₃ groups, believed to occur at temperatures >200°C. The copolyimide film broke into many very small pieces upon removalfrom the glass substrate, a sign that the molecular weight of thecopolyimide may be quite low.

Synthesis of the Copolyimide Directly from 6FDA, m-PDA, and 2,4-NaDBS(6FDAlm PDA12,4-NaDBS PI) A brownish dispersion of 2,4-NaDBS

(7.47 mmoles) and m-PDA (8.01 mmoles) in m-cresol (50 grams) andanhydrous toluene (20 grams) in a 3-necked flask equipped with athermometer, mechanical stirrer, and Dean Stark trap fitted with acondenser/nitrogen inlet was heated at about 150° C. under a nitrogenatmosphere. 6FDA (15.49 mmoles) was added to the hot dispersion,whereupon water immediately began to distill out of the reactiondispersion and become collected in the trap. The temperature of thebrownish dispersion was gradually increased to about 200° C., maintainedat 200° C. for 7.5 hours, and then decreased to ambient temperatures.The resulting dark brown colored, viscous reaction mixture was found tobe a dispersion containing significant quantities of crystallinematerial(s). The IR spectrum of the reaction dispersion showedabsorptions typical for or C=0 imide stretch (1781 and 1723 cm⁻¹), C—Nimide stretch (1365 cm⁻¹), SO₃ salt (1251 and 1033 cm⁻¹), and polyimide(738 and 720 cm⁻¹). The presence of m-cresol in the film preventsdetermination of whether HOSO₂ groups are present due to overlappingabsorptions. IR absorptions typical for polyamic acids at 1683 and 1548cm⁻¹ as well as the OH stretch of HOSO₂ were absent. IR data indicatedsome sodium sulfonate-copolyimide had been produced under the reactionconditions, but the presence of a crystalline dispersion rather thansolution suggests a significant amount of the diamine was notincorporated into a polymer.

The consistent problem encountered during these reactions was lowmolecular weight of the final product. The above syntheses did notprovide a creasable, sulfonated polymer film. However, fragments of thepolymer are unchanged by the peroxide test and have IECs up to 1.13meq./g.

It is anticipated that higher molecular weight polymer will be obtainedby further purifying the 2,4-NaDBS monomer prior to polymerization. Inaddition, the use of isoquinoline as a polymerization catalyst mayaccelerate the reaction.

EXAMPLE 6 Sulfonation of Victrex ® Poly(Ether Ketone) Using H₂SO₄/SO₃

Sulfonation Procedure II was used in the following example.

Procedure:

30.00 g PEK polymer (Victrex®) was dissolved in 270 g of concentratedsulfuric acid (93.5 wt. %) under nitrogen, stirred by an overheadmechanical stirrer. The polymer was dispersed over several days to forma dark red thick solution.

176 g of this solution was left in the three neck flask with overheadstirrer, N₂, etc. To the flask, 208.4 g of fuming sulfuric acid (25.5wt. % free SO₃) was added over the coarse of a few minutes with constantstirring to raise the solution to a free SO₃ content of 2 wt. %. Theresulting solution was immersed in a room temperature water bath tocontrol the temperature.

Samples were removed after approx. 1 hour, 3 hours, and 16 hours, andquenched into deionized water to precipitate.

In order to make films, the 1 and 3 hour products were washed severaltimes with deionized water, soaked overnight in approximately 0.5M NaOHsolution, then washed until a neutral pH was achieved. These wereblotted dry and placed in the vacuum oven overnight at 50° C. Driedsamples were dissolved in NMP to make a 20 wt. % solution. This requiredheating overnight at 60° C. Films of approx. 6 mils were cast onto afreshly cleaned glass plate. After two days of drying the films wereremoved by immersion into deionized water.

Soaking the films in water (at room temperature) caused considerableswelling to give a hazy gel-like consistency, but the 1 hour and 3 hoursamples did not dissolve. Film of the 1 hour product could be hydratedand dehydrated, while maintaining resistance to tearing. The 1 hoursulfonated PEK film IEC was measured to be 2.3 meq/g.

EXAMPLE 7 Sulfonation of PPS/SO₂ Using 97.5 % H₂SO₄

Sulfonation Procedure II was used in the following example.

PPS/SO₂ provided by James McGrath of VPI [see Synthesis andCharacterization of Poly(Phenylene sulfide—sulfone). Polymer Preprints38 (1), 1997, p.109-112].

Procedure:

250 ml 3 neck round bottom flask was equipped with an overhead stirrer,N₂ inlet, and addition funnel were charged with 100 grams of 93.5%sulfuric acid. To the rapidly stirring sulfuric acid 25.00 grams of thePPS/SO₂ was added. The mixture was stirred at room temperature until asolution formed (approximately 1 hour).

When solution had formed the temperature was lowered to about 0° C., and60.0 grams of 23.0% fuming sulfuric acid was added dropwise over aperiod of a 0.5 hours.

Ice bath temperatures were maintained for the first 3.5 hours of thereaction. Aliquots were taken at T=0.5, 1.5, 2.0, and 3.0 hours byprecipitation the reaction mixtures were precipitated into deionizedwater. Precipitated product appeared not to have swollen to anyappreciable extent, so the remaining reaction mixture was warmed to roomtemperature. Aliquots were taken at t=3:30, 4:30, 7:00, and 8:20(approximately 4 hours at room temperature).

Products were rinsed 3 times with deionized water, soaked in saturatedsodium bicarbonate solution until basic and then washed in deionizedwater until neutral.

Solubilizing of the sulfonated PPS/SO₂ polymers was attempted afterdrying the precipitated polymer at 100° C. for 3 hours under fulldynamic vacuum. The polymer solutions were made with fresh anhydrous NMPand were immediately cast on soda lime glass plates at a thickness of 2mils. The freshly cast films were placed in a level oven preheated to100° C. and dried under full dynamic vacuum for 1 hour. After drying (at100° C.) for an hour, the oven temperature was raised gradually to 200°C. over a period of 3 hours. When the 200° C. was achieved, the oven wasshut off and the films were permitted to gradually cool to roomtemperature. Films were removed from the glass plates by floating themin deionized water.

Based on crude observations of the PPS/SO₂ films, this material appearsnot to have sulfonated to any appreciable extent while kept at 0° C.(little dimensional changes were observed when boiled in water). ThePPS/SO₂ samples that were reacted at room temperature appear to showsome signs of sulfonation (swelling and taking on a rubbery appearancein boiling water).

IEC sulfonated PPS/SO₂:

T=8:20, 0.53 meq./g

Water Pick-up (wt. %) sulfonated PPS/SO₂:

T=8:20, 15%

Increased IECs of the sulfonated PPS/SO₂ samples should be possible withincreased reaction times.

EXAMPLE 8 Sulfonation of Poly(phenylquinoxaline)

PPQ was prepared as described in the literature (See e.g.,Macromolecular Syntheses, 1974, vol. 5 p.17), by dissolving equimolaramounts of an aromatic bisbenzildiketone and a bis-o-diamine in a 1:1mixture of m-cresol and xylene. The resulting polymer was isolated bydilution with chloroform followed by precipitation into a large excessof methanol. The polymer was thoroughly washed with methanol and vacuumdried.

Sulfonation was achieved by first dissolving this polymer inconcentrated sulfuric acid, followed by the addition of enough fumingsulfuric acid to react with any water remaining in the system (i.e. 100%H₂SO₄). The resulting solution was heated to 125° C. with constantstirring. Aliquots were taken over 6 hrs. at this temperature. Eachaliquot was isolated by precipitation into water, soaking in saturatedsodium bicarbonate, followed by several rinsings with deionized water.Sulfonation of the later aliquots was inferred from their enhancedsolubility in polar solvent systems. Generally, films cast of thesulfonated PPQ (sodium salt form) are tough, creaseable, and swell inwater.

Alternatively, a PPQ film can be soaked in a 50% solution of H₂SO₄ forapprox. 2 hour in order to fully sulfate it; then baked at a minimumtemperature of 300° C. to convert the ammonium sulfate salt to thecovalently bonded sulfonic acid. This procedure has been used for thesulfonation of PBI and PPQ films. See e.g., U.S. Pat. No. 4,634,530 andLinkous, et al., J. Polym. Sci., Vol. 86: 1197-1199 (1998).

EXAMPLE 9 Fabrication of SPEM Using PBO and Sulfonated Radel R®

Ion-conducting membranes were fabricated from the polymer substrate filmPBO and various sulfonated poly(phenyl sulfones). The substrate utilizedwas PBO film extruded and solvent exchanged into NMP as described abovein the general procedure. The ion-conducting polymer (100, 150%sulfonated Radel R®—Na+ form) was synthesized according to Example 1given above.

Microporous PBO, having been exchanged into NMP without collapse of thepores, was added to a 5 wt. % solution of the sulfonated Radel R®polymers in NMP. After twelve or more hours, the films were removed andplaced in a 20 wt. % solution of the same ion-conducting polymer (alsoin NMP). After twelve or more hours at room temperature (or at 75° C.)the films were removed, stretched in tensioning rings, and dried of thesolvent (see general procedure outlined above). Specifically, thesulfonated Radel R®/PBO films were dried in a low humidity chamber (<5%RH) for 1 to 2 days, vacuum dried in an oven heated from below 60° C. toabout 200° C.

After all solvent is fully extracted from the membrane, the composite ispreferably hot pressed. The hot pressing operation facilitates flow ofthe ion-conductor to make a homogenous composite structure. Non-porousTeflon® shims were placed on each side of the composite membranefollowed by Titanium shims. The entire setup is then loaded into a pressand subjected to the following cycle:

High Temperature Hot Press Step Temp. Hold Time Force Ramp Rate 1 392°F.  5 min  1.0 klb 15 F/min 2 392° F. 15 min 28.3 klb N/A 3  85° F.  5min 28.3 klb 25 F/min

Note that the 28.3 klbf corresponds to a press pressure of 1000 psi.

SPEMs produced via this example were FMI 126-17P, FMI 126-17Q, FMI126-17T, FMI 126-17U. See Table 8 for various results obtained fromSPEMs made via this procedure.

EXAMPLE 10 Fabrication of SPEM Using PBO and Sulfonated Udel®

Ion-conducting membranes fabricated in this example followed closelythose in Example 9.

The substrate utilized was PBO film extruded and solvent exchanged intoTHF as described above in the general procedure. The ion-conductingpolymer (75, 85, 100% sulfonated Udel®) was synthesized according toExample 4 given above.

For composite SPEMs of 100% sulfonated Udel® ion-conducting polymer,microporous PBO films exchanged into THF were placed into 30 wt. %solutions of the polymer (in THF) at room temperature. After more thantwelve hours, the films were stretched in tensioning rings and allowedto dry in a low humidity chamber. Final traces of the solvent wereremoved with the following vacuum pressing shown below.

Low Temperature Vacuum Pressing Step Temp. Hold Time Force Ramp Rate 1122° F. 20 min 2.9 klb 15 F/min 2 167° F. 20 min 2.9 klb 15 F/min 3 212°F. 20 min 2.9 klb 15 F/min 4 257° F. 20 min 2.9 klb 15 F/min 5  85° F. 5 min 2.9 klb 25 F/min

The force of 2.9 klb corresponds to a press pressure of 100 psi. Filmswere finally hot pressed without vacuum to fully consolidate thecomposite structure, as shown below.

High Temperature Hot Press Step Temp. Hold Time Force Ramp Rate 1 317°F. 30 min 28.3 klb 15 F/min 2  85° F. — 28.3 klb 25 F/min

The force of 28.3 klb corresponds to a press pressure of 1000 psi.

Composite SPEMs were made with both 75 and 85% sulfonated Udel®ion-conducting polymers.

SPEMs produced via this example were FMI 539-22-1, FMI 539-22-2, FMI539-22-3. See Table 8 for various results obtained from SPEMs made viathis procedure.

EXAMPLE 11 Fabrication of SPEM Using Solubilized Nafion® 1100 EW

Ion-conducting membranes fabricated in this example followed closelythose in Example 9.

The substrate utilized was PBO extruded film and solvent exchanged intoa mixture of water and alcohols (see below) as described above in thegeneral procedure. The ion-conducting polymer used was solubilizedNafion® 1100 EW purchased from Solution Technologies (10 wt. % in amixture of water and propanols). The solvent system used to exchange thePBO films was made to approximate that of the Nafion® solution.

Composite membranes were made by placing the exchanged films directlyinto the 10 wt. % Nafion® solutions. After twelve or more hours, thesewere removed and stretched into tensioning rings as described above.These films were dried in a low humidity chamber for at least 24 hours.Removal of the final traces of solvent were done by placing porous PTFEshims on each side of the composite membrane followed by the Titaniumshims. This setup was then loaded into a vacuum press and subjected tothe following cycle:

Low Temperature Vacuum Pressing Step Temp. Hold Time Force Ramp Rate 1125° F. 20 min 2.9 klb 15 F/min 2 170° F. 20 min 2.9 klb 15 F/min 3 215°F. 20 min 2.9 klb 15 F/min 4 274° F. 20 min 2.9 klb 15 F/min 5  85° F. 5 min 2.9 klb 25 F/min

The force of 2.9 klb corresponds to a press pressure of 100 psi. Filmswere finally hot pressed without vacuum to fully consolidate thecomposite structure, as shown below.

High Temperature Hot Press Step Temp. Hold Time Force Ramp Rate 1 275°F.  5 min  1.0 klb 15 F/min 2 275° F. 15 min 28.3 klb N/A 3  85° F.  5min 28.3 klb 25 F/min

The force of 28.3 klb corresponds to a press pressure of 1000 psi.

SPEMs produced via this example were FMI 126-16N, FMI 126-160. See Table8 for various results obtained from these SPEMs. The low IECs obtainedfrom these films and the correspondingly high resistances are a functionof the low loading of ion-conductor in the composite structure. It isanticipated that using more concentrated solutions of the ion-conductorin imbibing the substrate will lead to composite SPEMs of low enoughresistances for the applications described. The stability of the lateraldimensions of these Nafion® based composite membranes presents asignificant improvement over unsupported Nafion® 117 films (which showin plane dimensional changes on hydration of about 20%). Given theexceptional strength of the PBO substrate, the mechanical properties ofthe composites are well in excess of current state of the art fuel cellmembranes.

EXAMPLE 12 Fabrication of SPEM Using PBO and sulfonated Ultrason®

Ion-conducting membranes fabricated in this example followed closelythose in Example 9. The substrate utilized was PBO film extruded andsolvent exchanged into NMP as described above in the general procedure.The ion-conducting polymer (75% sulfonated Ultrason purified—Na+ form)was synthesized according to Example 3 given above.

Microporous PBO, having been exchanged into NMP without collapse of thepores, was added to a solution of the sulfonated 75% sulfonated Ultrasonpolymer in NMP (8 or 12 wt. %). After twelve or more hours at roomtemperature the films were removed, stretched in tensioning rings, anddried of the solvent (see general procedure outlined above).Specifically, the sulfonated Radel R®/PBO films were dried in a lowhumidity chamber (<5% RH) for 1 to 2 days, vacuum dried in an ovenheated from below 60° C. to 140° C.

Low Temperature Vacuum Pressing Step Temp. Hold Time Force Ramp Rate 1125° F. 20 min 2.9 klb 15 F/min 2 200° F. 20 min 2.9 klb 15 F/min 3 275°F. 20 min 2.9 klb 15 F/min 4 390° F. 20 min 2.9 klb 15 F/min 5  85° F. —2.9 klb 25 F/min

The force of 2.9 klb corresponds to a press pressure of 100 psi. Filmswere finally hot pressed without vacuum to fully consolidate thecomposite structure, as shown below.

After all solvent is fully extracted from the membrane, the composite ispreferably hot pressed. The hot pressing operation facilitates flow ofthe ion-conductor to make a homogenous composite structure. Non-porousTeflon® shims were placed on each side of the composite membranefollowed by Titanium shims. The entire setup is then loaded into a pressand subjected to the following cycle:

High Temperature Hot Press Step Temp. Hold Time Force Ramp Rate 1 390°F. 15 min 28.3 klb 15 F/min 2  85° F.  5 min 28.3 klb 25 F/min

The force of 28.3 klbf corresponds to a press pressure of 1000 psi.

SPEMs produced via this example were FMI 126-08E, FMI 126-08F. See Table8 for various results obtained from SPEMs made via this procedure.

EXAMPLE 13 Fabrication of SPEM Using Cast PBO and Sulfonated Radel R®

Ion-conducting membranes can be fabricated as illustrated above inExample 12 with use of microporous PBO substrates obtained by the filmcasting techniques enumerated in the general procedures. These filmswere solvent exchanged from water into NMP, after the coagulation andrinsing. These microporous films were placed in ion conductor solutions(5-10 wt. % in NMP) and allowed to equilibrate for a day or more. Onceinfused with the ion conductor solution, the films were placed intensioning rings and dried of the solvent. In the case of the sulfonatedRadel R®/cast PBO films, samples were first dried in a low humiditychamber for 1 or more days at room temperature and then vacuum dried at200° C.

After all the solvent had been dried from the membrane, the compositestructure was hot pressed using methods similar to those in Example 9.SPEMs produced via this example were FMI 126-AY1, FMI 126-82BE and FMI126-d91BO. See Table 8 for various properties of these compositemembranes.

EXAMPLE 14 Fabrication of SPEM Using Microporous Poly(ether sulfone)Substrate and Nafion® 1100EW Ion Conductor

A commercially available microporous membrane made of poly(ethersulfone) was obtained from Memtec (BTS-80), with a 0.02 micron pore sizeand an approximate porosity (void volume) of 80%. This microporousmembrane was soaked in a Nafion® 1100 EW solution (water/alcoholsolvent). A vacuum was drawn on the solution and film to degas andcompletely fill the pores. The film was then removed from the solutionand vacuum dried (to approx. 100° C.). This process was repeated twomore times, each time the film was added to the solution, vacuumdegassed, and dried of solvent. Finally, the ion-conducting componentwas placed in the sodium salt form by soaking in saturated sodiumbicarbonate solution by repeated rinsing followed by vacuum drying.Properties of a SPEM produced sing the above method are shown for FMI126-79BB in Table 8.

EXAMPLE 15 Crosslinking of Sulfonated PPSU

Ion-conducting polymeric samples can be crosslinked in the acid (H+)form to improve ICP stability. Normally, crosslinking is performed invacuum, to exclude oxygen from the system (can cause ICP charring). Forexample, SPPSU was crosslinked in a vacuum oven preheated totemperatures of 200, 225 and 250° C. for durations of up to 8 hours.Under these conditions, samples showed a slight IEC loss (−10%), andlittle improvement in long term stability (peroxide test). More severeconditions were employed by exposing samples to 250° C. in full vacuumfor more than 20 hours. Peroxide testing did not show any considerabledifference between SPPSU crosslinked films and SPPSU controls untilheated for at least 32 hours. The SPPSU films crosslinked at 250° C. for32 hours and 72 hours maintained their film integrity during theperoxide accelerated life test. The IEC of these test samples decreasedsignificantly. Specifically, a loss of 63% (1.90 to 0.69 meg/g) for the32 hour sample and a loss of 73% (1.90 meg/g to 0.51 meq/g) for the 72hour crosslinked SPPSU films was calculated. It is anticipated that manyof the SO₃H acid groups form aromatic sulfone (Ar—SO₂—Ar) crosslinksbetween polymer chains. This trend confirms that crosslinking (H+ form)of sulfonated polymers can be used to improve long term membranestability.

What is claimed is:
 1. A composite solid polymer electrolyte membrane(SPEM) comprising a porous polymer substrate interpenetrated with anion-conducting material, wherein the SPEM is substantially thermallystable to temperatures of at least about 100° C., and wherein (i) theporous polymer substrate comprises a homopolymer or copolymer of aliquid crystalline polymer or a solvent soluble thermoset orthermoplastic aromatic polymer, and (ii) the ion-conducting materialcomprises a homopolymer or copolymer of at least one of a sulfonated,phosphonated or carboxylated ion-conducting aromatic polymer or aperfluorinated ionomer.
 2. The SPEM of claim 1, wherein the SPEM isstable from at least about 100° C. to at least about 175° C.
 3. The SPEMof claim 1, wherein the SPEM is stable from at least about 100° C. to atleast about 150° C.
 4. The SPEM of claim 1, wherein the SPEM is stablefrom at least about 120° C. to at least about 175° C.
 5. The SPEM ofclaim 1, wherein the SPEM is substantially stable to temperatures of atleast about 120° C.
 6. The SPEM of claim 1, wherein the ion-conductingmaterial comprises at least one of a polystyrene sulfonic acid (PSSA),poly(trifluorostyrene) sulfonic acid, polyvinyl phosphonic acid (PVPA),polyacrylic acid and polyvinyl sulfonic acid (PVSA) polymer.
 7. Acomposite solid polymer electrolyte membrane (SPEM) comprising a porouspolymer substrate interpenetrated with an ion-conducting material,wherein (i) the porous polymer substrate comprises a homopolymer orcopolymer of a liquid crystalline polymer or a solvent soluble thermosetor thermoplastic aromatic polymer, and (ii) the ion-conducting materialcomprises a homopolymer or copolymer of at least one of a sulfonated,phosphonated or carboxylated ion-conducting aromatic polymer or aperfluorinated ionomer.
 8. The SPEM of claims 1 or 7, wherein the porouspolymer substrate comprises a microinfrastructure substantiallyinterpenetrated with the ion-conducting material.
 9. The SPEM of claims1 or 7, wherein the porous polymer substrate comprises an extruded orcast film.
 10. The SPEM of claims 1 or 7, wherein the liquid crystallinepolymer substrate comprises a lyotropic liquid crystalline polymer. 11.The SPEM of claim 10, wherein the lyotropic liquid crystalline polymersubstrate comprises at least one of a polybenzazole (PBZ) and polyaramid(PAR) polymer.
 12. The SPEM of claim 11, wherein the polybenzazolepolymer substrate comprises a homopolymer or copolymer of at least oneof a polybenzoxazole (PBO), polybenzothiazole (PBT) andpolybenzimidazole (PBI) polymer and the polyaramid polymer comprises ahomopolymer or copolymer of a polypara-phenylene terephthalamide (PPTA)polymer.
 13. The SPEM of claims 1 or 7, wherein the thermoset orthermoplastic aromatic polymer substrate comprises at least one of apolysulfone (PSU), polyimide (PI), polyphenylene oxide (PPO),polyphenylene sulfoxide (PPSO), polyphenylene sulfide (PPS),polyphenylene sulfide sulfone (PPS/SO₂), polyparaphenylene (PPP),polyphenylquinoxaline (PPQ), polyarylketone (PK) and polyetherketone(PEK) polymer.
 14. The SPEM of claim 13, wherein the polysulfone polymersubstrate comprises at least one of a polyethersulfone (PES),polyetherethersulfone (PEES), polyarylethersulfone (PAS),polyphenylsulfone (PPSU) and polyphenylenesulfone (PPSO₂) polymer; thepolyimide (PI) polymer comprises a polyetherimide (PEI) polymer; thepolyetherketone (PEK) polymer comprises at least one of apolyetherketone (PEK), polyetheretherketone (PEEK),polyetherketone-ketone (PEKK), polyetheretherketone-ketone (PEEKK) andpolyetherketoneetherketone-ketone (PEKEKK) polymer; and thepolyphenylene oxide (PPO) polymer comprises a 2,6-diphenyl PPO or 2,6dimethyl PPO polymer.
 15. The SPEM of claims 1 or 6, wherein the poresize of the porous polymer substrate is from about 10 Å to about 20,000Å.
 16. The SPEM of claim 15, wherein the pore size is from about 10 Å toabout 2,000 Å.
 17. The SPEM of claim 15, wherein the pore size is fromabout 500 Å to about 10,000 Å.
 18. The SPEM of claims 1 or 6, whereinthe ion-conducting material has an ion-conductivity from about 0.01 S/cmto about 0.50 S/cm.
 19. The SPEM of claim 18, wherein the ion-conductingmaterial has an ion-conductivity greater than about 0.1 S/cm.
 20. TheSPEM of claims 1 or 7, wherein the ion-conducting aromatic polymercomprises wholly aromatic ion-conducting polymer.
 21. The SPEM of claim20, wherein the sulfonated wholly-aromatic ion-conducting polymercomprises a sulfonated derivative of at least one of a polysulfone(PSU), polyphenylene oxide (PPO), polyphenylene sulfoxide (PPSO),polyphenylene sulfide (PPS), polyphenylene sulfide sulfone (PPS/SO₂),polyparaphenylene (PPP), polyphenylquinoxaline (PPQ), polyarylketone(PK), polyetherketone (PEK), polybenzazole (PBZ) and polyaramid (PAR)polymer.
 22. The SPEM of claim 21, wherein (i) the polysulfone polymercomprises at least one of a polyethersulfone (PES),polyetherethersulfone (PEES), polyarylsulfone, polyarylethersulfone(PAS), polyphenylsulfone (PPSU) and polyphenylenesulfone (PPSO₂)polymer, (ii) the polybenzazole (PBZ) polymer comprises apolybenzoxaxole (PBO) polymer; (iii) the polyetherketone (PEK) polymercomprises at least one of a polyetherketone (PEK), polyetheretherketone(PEEK), polyetherketone-ketone (PEKK), polyetheretherketone-ketone(PEEKK) and polyetherketoneetherketone-ketone (PEKEKK) polymer; and (iv)the polyphenylene oxide (PPO) polymer comprises at least one of a2,6-diphenyl PPO, 2,6-dimethyl PPO and 1,4-poly phenylene oxide polymer.23. The SPEM of claims 1 or 7, wherein the ion-conducting aromaticpolymer comprises a sulfonated, phosphonated or carboxylated polyimidepolymer.
 24. The SPEM of claim 23, wherein the polyimide polymer isfluorinated.
 25. The SPEM of claims 1 or 7, wherein the perfluorinatedionomer comprises a homopolymer or copolymer of a perfluorovinyl ethersulfonic acid.
 26. The SPEM of claim 25, wherein the perfluorovinylether sulfonic acid is carboxylic- (COOH), phosphonic- (PO(OH)₂) orsulfonic-(SO₃H) substituted.
 27. The SPEM of claims 1 or 7, wherein theporous polymer substrate comprises a homopolymer or copolymer of atleast one of a substituted or unsubstituted polybenzazole polymer, andwherein the ion-conducting material comprises a sulfonated derivative ofa homopolymer or copolymer of at least one of a polysulfone (PSU),polyphenylene sulfoxide (PPSO) and polyphenylene sulfide sulfone(PPS/SO₂) polymer.
 28. The SPEM of claim 27, wherein the polysulfonepolymer comprises at least one of a polyethersulfone (PES) andpolyphenylsulfone (PPSU) polymer.
 29. The SPEM of claims 1 or 7, whereinthe SPEM has a specific resistance from about 0.02 to about 20Ω*cm². 30.The SPEM of claims 1 or 7, wherein the SPEM has a specific resistance ofless than about 0.2Ω*cm².
 31. The SPEM of claims 1 or 7, wherein theSPEM has a thickness from about 0.1 mil. to about 5.0 mil.
 32. The SPEMof claim 31, wherein the thickness is about 1 mil.
 33. A devicecomprising a composite solid polymer electrolyte membrane in accordancewith claims 1 or
 7. 34. The device of claim 33, wherein the device is afuel cell.
 35. The device of claim 34, wherein the fuel cell is a directmethanol fuel cell or a hydrogen fuel cell.
 36. The device of claim 35,wherein the direct methanol fuel cell has a methanol permeation rate ofless than about 50 mA/cm² of equivalent current density at 0.5V.
 37. Thedevice of claim 34, wherein the fuel cell is used to supply power to anelectronic device.
 38. The SPEM of claims 1 or 7, wherein theion-conducting material comprises sulfone crosslinkages.
 39. The SPEM ofclaims 1 or 7, wherein the ion-conducting material is chlorinated orbrominated.
 40. The SPEM of claims 1 or 7, wherein the ion-conductingmaterial comprises one or more antioxidants.